I think Kelly's fame is a big motivator for the BM. If BM is super-duper friendsies with her ex and Kelly, then she's relevant to someone famous and she gets interviews and fame by association.

Kelly has inherent power over the BM because of this, the BM knows this and is acting accordingly. She is recognizing Kelly as the wife of her ex, and not treating her as some second-rate replacement. She is recognizing the child as part of her kids' family. Most of us on ST don't have BMs like this, because the BM feels like she holds power over the SM.

These interviews with the media wouldn't gain her any attention at all if she said "Meh. I'm glad they're happy and wish them well with the new baby. Generally, I leave them alone and they leave us alone." That wouldn't get published and the BM wouldn't get any positive attention for how wonderful she is (like this very post.) Also, if she were acting like a wicked witch, she certainly wouldn't be publicizing that, either.

Just saying this isn't a normal situation, and I doubt things would be SO incredibly wonderful and peachy if Kelly were just another non-famous stepmom. The dynamics here almost require the BM to suck up to Kelly and her ex-husband.

(... BRB. Figuring out how can I become a celebrity so our BM will shut the eff up.)