Potentially unpopular opinion here, but its is because the power equation has shifted so far in the direction of the female in a marriage. It used (in an idealized classical sense) to be that once married, women needed men for financial support and physical security, and men needed women to create a home and bear and raise children. In a divorce scenario, women would lose financial support, and men would lose a sense of a home (and access to regular sex).

Now, a stay at.home mom can divorce her husband for whatever reason strikes her, and receive half of the net assets AND half or more of her former husbands Future inclme through alimony and child support (and child