Science

Otherwise mom would be just happy to say, "Naw, I want those resources, die."

Recently read about a species of pipefish where the males have developed a pouch. The female lays eggs and the male carries them and provides nutrients for them (or maybe just can siphon off nutrients from the embryos' stash?).Anyway, apparently the male controls the food supply. Lots of food available to the adult, happy healthy baby pipefish. Dad's body doesn't think there's enough food, the first thing to go are the young--first stunted, then dead.

If not for the "guy" gene in the human fetus, humans would be like pipefish. But our brains are at least a few % bigger, so 'stunted' would mean a lot of cognitively impaired kids being born. Human biology favors continuing the species quite a bit more than that.