I first read about this concept about a dozen years ago. The article I read was about the possibility of first creating African elephant/mammoth hybrids, in part to lead to the creation of an animal that could handle the size of a "pure" mammoth. The article also proposed that such animals might be sold as a food source, in part to justify their de-extinction. The target audience for the article seemed to be high school kids, so I'd guess that the food idea was at least partly a joke.

It's an interesting idea to bring these animals back, but what would it take to create the kind of wildlife management system and corps of personnel to effectively manage wild populations of these animals? Mammoths among other megafauna likely had large ranges. In modern sanctuaries, this is often a problem, or so I'm given to understand. In addition, given the widespread leeching of chemicals and man-made pollutants like plastics into groundwater and into plant life, how might that affect these animals?

Another problem is that large predators need lots of meat. Are there stable enough populations of prey animals to support them, or would populations of prey animals need to be established? If so, what would they eat? Would they compete with existing species?

Out of curiosity, why don't you support the de-extinction of Neanderthals? Do you feel that way about all extinct hominids?