My opinion is that a mid-life crisis is caused by years of the father's wants and needs not being fulfilled. The saying that women and children come first applies pretty much equally throughout all of society, including when it comes to marriage and child care. Women sacrifice a lot in a marriage and for their children. But their sacrifices are recognized and rewarded. They are encourage to "treat themselves" because "women only ever think about other people and not themselves".

Well a husband / father sacrifices just as much. But he's never encouraged to do anything for himself because society has this jaded view that men are selfish. And after a couple of decades of literally never doing anything for himself, never taking time for "self-care" or to "treat himself" the way women usually do, he finally snaps and has a mid-life crisis.

Which is basically just him deciding to treat himself, for once in his life, after decades of not being able to.