Because the courts ALWAYS gave women the kids. It hasn't been till the last 15 years that courts are starting to see women aren't the better parent and they should be equally reviewed. 

So for decades, men didn't have a choice.  You probably still believe abuse and such at home is mostly from the father... but you would be wrong. Guess what, women are just as nasty, look at the real crime stats. 1/2 of all domestic violence is done by the women. But people like you conveniently forget the realities.