In some twisted way, my ex-wife assumed that she was the better parent and thus more entitled to the child support, the house, and the kids' care and feeding. As a good dad, this was just her assumption. Today, her assumption wound probably be supported by state family law. But, I believe times are changing.
My ex knew I would not sue her for 50/50 custody. She didn't want to lose 50% of the time with her kids. 30% sounded almost palatable. Painful, but well worth the freedom she imagined just ahead, as she headed towards becoming a single mom.