Statistically, fathers who ask the courts for joint custody almost always receive it. Occam's Razor dictates these men you know most likely prefer to complain about their divorce rather than to do the arduous work of parenting. They can also renegotiate this circumstance if they feel like it.
or the parents really just don't get along. seriously, i'd rather give up my kids than deal with a horrible partner. if i could deal with her, why even get a divorce (unless the partner pushes for it)? i am glad that my parents did not get joint custody when they divorced. it would have been a disaster.