People want to eat meat. Pink slime is a small amount of meat with large amounts of the bits you'd normally leave behind.

I'm not against mechanically recovered meat. But I'd prefer children to get chunks of real meat cooked well than a squirt of slime and salt and flavourings in a crumb coating which is then fried and served with a sugary sauce. (ketchup, bbq, etc.) That combination of fat, salt, and sugar makes food "hyper palatable"[1] and, while much cheaper than "real" food contains little in the way of useful nutrition.

[1] Not my term. It's used to describe food where the balance of salt, sweet, and fat have been carefully balanced, and where the food is very easy to eat, because it's small or soft and easy to chew. See the progression from roast chicken, to deep fried chicken, to deep fried chicken with a salty coating and sauces, to "popcorn chicken" which are small chunks of meat, with a lot of fat-soaked salty coating.