He doesn't need to if they do shared custody where they each have the kids the same amount. But if he just ups and leaves, why should she be left holding the bag? They're his kids. She didn't make them by herself. It's his responsibility to support them.
Why does the law send guys who refuse to financially support their kids to jail, because it was happening so often that women were simply left holding the bag, left to support the kids all on their own while the guys just went about with their higher incomes not supporting them at all that it created a social injustice so massive, and a government expense since many of these kids were ending up on welfare roles specifically because their dads were being deadbeats, that the government stepped in and had to make the penalty for not fulfilling your parental responsibilities something you can go to jail for, which it already was that way as child neglect, failing to feed and clothe your children, was already criminal.