It's not as simple as that thought is it. No one sets our to put themselves in these situations. It's like saying to someone why did you stay when they are in an abusive relationship it's not always as easy as just walking away.
Normally these situations grow over time, you don't wake up one day and decide to live that way.
You start a relationship, they say one say you'll be married, this seems reasonable, before you know it there is a child and now he's convinced you that he cares ever so much about that child that you should stay home and he will pay for this... Etc.
Before I was with my husband I was in a relationship with someone who before we bought out house together told me he wanted to marry me, we would have a child. The bills were all in my name and I paid them all. He contributed a small amount overall, and as his wages increased I didn't ask for anymore because we talked about him savings for our future. Was I naive, yes, but did I walk into that situation from day one, no, it grew over time.
Long story short he left,l for another women, luckily I managed to remortgage without him and buy him out. But it was hard because I had almost no savings as I had been paying for everything niavely on the basis he was the one with the savings for emergencies.
It's a form of emotional and financial abuse and it's easy to fall into without noticing until you are knees deep in it.