I have two games where the woman works a lot harder than the man and gets promoted more often. They don't get promoted automatically either, they get a promotion when they fill their progress bar by working. I also have a man who is always dusting the furniture and cleaning the nightstand, and he even takes the trash out without being asked I think the inequality you see is a random combination of traits in your families.
Also remember that a lot of kids are playing these games. How would they react if they made their little family make a baby and all of a sudden daddy has one in his arms? Might raise some questions ^^
I do agree it would be nice if the father could take over for a bit and help in taking care of the baby, but I suspect the mechanics for that are a lot more complicated than it sounds.