What I do think is that some of the women on here can't see the cause or their problem
I know what you're saying, I'm often shocked by the cheek of the DH/P in threads on here. But as long as there are pages and pages of comments on any thread where a SM expresses anything other than unfailing positivity about the situation, saying things like "you knew what you were getting into", "you will never be as important as the kids, you known your place", calling her childish for wanting any amount of time with her partner (even if he's currently not spending any with her and it's a perfectly rational feeling), calling her selfish for having subsequent children with him that are just a hindrance to his first ones, saying they would kick her to the curb if they were here partner and she ever dared to tell their child off or didn't love them "as much as her own" - the partner is not the only problem. The attitudes of people in general are a major part of the problem.
It is normalised for separated parents to get into relationships with new people and expect them to put up with things they would never put up with in other relationships, without ever struggling with that. It's normalised for them to expect their partner to be down with doing half if not more of the childcare because after all, they should "love them like their own", and if they don't then THEY are the problem. It's normalised to be incredibly defensive of any perceived criticism of the children's behaviour, or of the things the step parent is being expected to put up with for the sake of the children.
Yes you get a lot of Disney dad's, but the problem runs so much deeper than that. The problem is the culture that allows them to act that way, putting step parents at the absolute bottom of the pile, whilst also having the nerve to vilify them for it, when in reality all a step parent is on paper is someone that didn't reject a potential partner on the basis of THEIR past choices. It is incredibly isolating to do that with no malice in your heart, only to find that you are living in a society that hates you. In my opinion, it makes the situation 10x harder to deal with and probably leads to the resentment everyone is so afraid step parents are going to exhibit. I know I would find it much easier to deal with if I wasn't forever railing against the injustice of it all.