There are two aspects here. One is child care, although here I think the USA does much better than many other countries where the judge simply gives the children to the mother by default, and often even very strong arguments don't help.

The other issue, probably more relevant, is that you split all you have in half (roughly). In theory, it is to make up for the fact that the woman has to deal with childbirth and all the consequences, including missed opportunities. In practice it means that even if you don't have any children, you need to give her half of everything if she decides so. Some people consider it very unfair, but of course every situation is different.

The fact is, women file for divorce more often than men, and not everybody is comfortable with a prenuptial agreement arguing that marriage is based on trust, and if you don't have that trust at the beginning, why to marry at all?

EDIT: Theory aside, when you read about particular cases like this one, they are depressingly sobering: https://www.quora.com/Why-do-most-women-have-the-advantage-d...