The FDA does regulate, but much more lightly - from their site:

"The FDA’s regulation of pet food is similar to that for other animal food. There is no requirement that pet food products have premarket approval by the FDA. However, the Federal Food, Drug, and Cosmetic Act (FFDCA) requires that pet foods, like human foods, be safe to eat, produced under sanitary conditions, contain no harmful substances, and be truthfully labeled."

I'd hope they care at least some. Little kids love to eat dog/cat food and treats, and it's hard to keep them out of it. At least enough to make sure it's not, like, full of lead or something.