Why do the law have the appetite to fight for father's rights?

it's not just limited to non-custodial parents...i have one child that lives with me who i am supposed to get child support for...but have only recieved 500 dollars for in the last two years. while at the same time i pay child support on another child. since the mother of the child that lives with me won't pay, i fall behind on my payments for the other. then come tax time the ag takes her tax refund and gives it to the other child. we get nothing.