Childfree here, and I think it might be a side effect of having to do a lot of thinking about society against the current.

Having children is a lot of work that often gets romanticised and oversimplified, so once you look at it really hard it’s no longer that obvious of a good decision. Sexist men also have no concept of how hard it is to both give birth to and raise a child, so if you’re a man and generally think women deserve rights, I bet you’ll be more conscious about that.