Because it's even more ridiculous than raising normal animals for food. Producing a whole animal minus a functional brain is no less wasteful than raising a normal animal and you have the added expense of developing this tech (which, granted, goes to zero with time). We can already grow meat without actual animals, just using animal cells, and even engineering meat from completely plant tissue is viable. And that's for the case someone is psychologically “desperate” for meat as such, because we don't really need any animal products in our diet.