Because they don't have kids, but they have a hole in their soul that wants kids, so they substitute dogs for kids, like substituting living together for marriage, and pretend their dog is a kid, and form unhealthy and dysfunctional attachments to their dog, so naturally, split custody makes sense to these insane people.

It reminds me of women who never became mothers, and have the unmet need to mother children, so they get into government to "mother" the electorate.