Why don't people cultivate endangered species like they do cattle?

African elephants, certain species of tiger, and all species of rhinoceros are on the verge of extinction. Poachers keep killing the few remaining. Why don't entrepreneurs cultivate populations to meet the market demand for elephant, rhinoceros, and tiger products?

I understand that these animals eat a lot, but so do cows. I assume elephants and rhinoceros are edible.

This seems like a way you could remove these species from the endangered species list and potentially make the animals in the wild safer. Maybe there are other endangered species that could be saved in this way.

What barriers exist besides the regulations and protections on these animals?