If you have read in any depth on here, I think you will probably be able to answer most of your own questions, or maybe they are rhetorical.
DH's by and large, want the SKIDs to love them, and some are so afraid that if they exert some discipline and set boundaries, the SKIDs will reject them. This is a fallacy, of course, but we have a lot of Disney Dads who believe it, and who are unable to be an adult and a parent but try to be BFF with their kids.

I don't think moving out is a "strategy" to get them to take the situation seriously, speaking as one who has contemplated this as a final solution - I told my DH one time (in 10 years of hell) that I was close to not being able to tolerate the drama and nonsense any longer. Most of us love our DH's dearly despite their indifferent parenting skills, and will put up with a lot in order to be with them. But everyone has their bottom line, and sometimes the stress is not worth the positive aspects of staying married.

That's a large question:

1. A woman work is to take care of children.
2. Fear that the child(ren) will say "I don't want to visit you anymore".
3. See # 2.
4. Nothing else has worked so far.

Of course there are exceptions to everything. I've simplified these answers so you'll just have to follow along to flesh out the problems and solutions and yes unsoluable situations.

And please don't think I'm advocating or not advocating anything I've just listing the reasons. Prejudices about what the fameles role in life still abound.

I did what I now know to be 'disengaging' and it worked out for me. Obviously there are some things that I still needed to know about SKids, if it impacted me directly. Other than that I tried to instill self discipline into them but, and this is a huge BUT here, SKids are sociopaths, just like their mother, and only one of them has an actual diagnosis of 'borderline personality disorder'. The one being SD, who was the worst juvenile case they had on file! I had to disengage, for my own sake! It's not always bad parenting that is to blame, there are bad seeds and eggs!
I did consider parenting SKids initially, regular parenting style did not work! I consider holding kids accountable and showing them the way to do stuff that is more generally acceptable to be a reasonable parenting style and it worked for my bio three. My style went down like a lead balloon here! Parenting sociopaths is hard, damn hard, so I stopped it. I created my own boundaries with them, I was labelled a bitch and blamed for all their misfortunes but I can live with that...one day they might just realize? Not hanging on by my fingernails for that one!
I believe that we are all individuals and our kids do not define us as people. We have to maintain our individuality throughout our lives. I understand that we can get wrapped up in stuff but our basic selves are still in there. I rode out the storms, it was hell on wheels at times, now the SKids have left home and we have some peace. They are not out of mind just because they are out of sight though, I believe a parent still thinks about kids beyond their childhood, or am I wierd? LOL. Just not having them underfoot is a distinct plus though. Assigning blame is a tricky one, DH was, still can be at times, the Disney dad and I am gradually putting boundaries down for him too. I tell him that I am getting tired of them taking advantage of US, I mean him but it's more palatable when I say us. He wanted them to have a 'childhood' and that was his justification, well, they are not children any more, they are 19, and they are working and need to learn how to take care of themselves. My belief is that we need to raise our kids to become independant adults. I considered long and hard what my role should be with step kids and I decided that, even though I did not agree with DH's parenting style, that they are his kids. I lessened the impact on me and the confusion for the SKids. The juvenile justice system tried hard to hold SD accountable and they failed miserably too! It's about the kids, really, there is no 'one size fits all' parenting in the fullest. There are moral codes and guidelines to follow for decency and fitting into society.

For an abusive situation to continue there is someone doing the abusing and someone who is tolerating being abused.

Sometimes it is hard to read of situations where the stepparent is so beaten down with no rights. And I know it is hard to leave if one has no financial resources.

But what amazes me is when some women (or men) actually support a deadbeat partner and skids who all treat her like dirt. That's very self destructive.

Unfortunately, there are a lot of mothers who think that taking care of their biological children is someone else's responsibility. Like stepmother's or exclusively biological father.
I say...you are not able to take care of another human being beside yourself( a baby), don'r bring them into this world. Or if you brought them into this world and you are not able to care for them, allow someone who is able and that is it.
Some BMs and some fathers as well out there are afraid that disciplining the child will make them look bad and the child will not love them anymore. Children need rules/discipline. guidance. They don't need the parents to be their friends.

Question 1:

Why do I read so many stories of how the DHs expect the step moms to take care of and or be second to the skids?

In my case, in the beginning of our relationship, once we had moved in together, DH had been living with his overbearing all controlling mother and she was the parent to skid 100%. He expected and assumed that I would step in and do the same. He also thought that since he screwed up royally by reproducing with a worthless waste of space, that in me, he had found the "right" wife and "right" mom for skid. In regard to the being second to the skid, I don't get it either. I was not raised this way. I had good parents and a nice life, but I was never doted on nonstop and I never felt like I was second on the totem pole under my father and my mother being second to me and my needs.

DH's parents are the exact opposite. I would not even call their marriage a marriage. She has 4 kids with DH's dad, but DH's dad is not her partner, he is pretty much the 5th kid. She does not treat him like an equal in their home, her kids and now skid, are all she cares about. She bragged to me once that after she had her first child, she looked FIL dead in the eye and told him the days of their lives being about each other were over, that her kids will come first, and her marriage second, and that was that. FIL pretty much does not even exist to MIL and DH says it has always been that way. He is just the guy in the recliner. There is no love, no intimacy, no closeness between them at all, but she goes above and beyond normal levels with her kids. I used to feel sorry for FIL. Not anymore, because he does nothing about it and is clearly the most whipped man alive.

DH does not like how he sees his father live, but he does the same thing to me and treats skid the same way, always first, and I am always on the backburner. My DH is the same way with MIL. She has total control of him and he ever questions it. This has had a huge impact on my DH's way of thinking. He has so much pent up resentment and anger towards his mother that he is hyper vigilant when it comes to me. When he even thinks for a second that I am trying to control him, even if I am not, even if I am just making a suggestion that would benefit him, he blows up.

Question 2: Why are there so many DHs without the back bone to stand up to the skids and enforce the hierarchy and discipline in the home?

I love the way you worded this, the hierarchy of discipline. That is how it was when I was a kid. My Dad was the boss. He had an iron backbone. He and my Mother were partners, friends, they were on the same level, if you crossed Mama, you got to deal with Daddy and vice versa. They never ever undermined one another, and as kids, we respected that. The no back bone thing is a huge deal for me. My DH has zero balls when it comes to skid and MIL. Now with me and other people, he has not trouble asserting himself, but with those two, not a chance. I believe, at least with my DH, that with skid, it boils down to he is on a quest to make sure skid favors him over the BM, and in his idiotic head, he thinks that the key to this is to let skid run the show, run over him, run over me, make us miserable, but skid is happy so he is winning.

Question 3: Why are stepmoms feeling like they cant live in their own homes because of skid drama?

I contemplate moving out because to me, that is the only way I would ever be free of all of this. Sometimes I get so overwhelmed by the stress and the grief over how disappointed I am in my marriage, in my DH, in myself, that I think being alone is a better alternative to continuously being subjected to the disgust.

Question 4: Why does moving out come up as a strategy to try to get the DH to take our situation seriously?

I think with me, part of me just hopes that if he were to experience losing me, have that cold reality set in, that maybe he would wake up and make some changes. Wishful thinking most likely though.