re: OP - Because it's nice and comfy for them! He gets to spend all the money, have dominant sex with as many people as he wants, stroll around in freedom with his nice ironed shirts and stuff. What's not to like?
re: Why we stay(ed) - Because abuse:-
a] Starts small and works up, insidiously. Like dry rot.
b] Uses love to get what it wants. Love will make many sacrifices, especially when they're small to begin with.
c] Lies, in its words and its actions. It tells you what you want to hear; it gives you nice presents; it makes your children laugh.
d] Cheats. It tricks you, puts you on the back foot and makes you doubt the evidence of your own senses.
e] Fills you with fear, so you eventually believe you cannot leave.
f] Relies on social pressures. Society likes married couples with families. Society will overlook many warning signs, because society feels safer when its people are married with families.
g] Is assisted by sexism. When a man is abused by a woman, he may feel shamed and few outsiders will believe him. When a woman is abused by a man, there's no shortage of advisers telling her she's got it all wrong and he's just being a man.
While I feel very strongly that men do still enjoy more entitlements, and a stronger sense of entitlement, than women - I don't think that has anything to do with abuse. Abusers are bullies. You find more men bullying women (or, more noticeably) because the strength differential affords power. There are plenty of female bullies around, too.