Why do women get custody of the kids, automatically, in a divorce?

I've always found this to be incredibly unjust. I don't have kids, am not married, but I've seen so many solid dudes, and great dads have their life absolutely fucked up by their ex. <br><br>I've heard that this may be changing, but the courts still lean heavily towards the mother, simply because she's the mother, in most cases.<br><br>In a way, I kinda get it, because it's generally better for the kids to have their mother, especially if they're young. But what about all the useless mothers? Where the father is the better parent? Also, why do they have to pay child support? If the mother has full custody, it's not like they even get to spend time with their children anymore, so it's not like they have to support them.