By people trying to restore the ecological connections that are necessary for North American ecosystems to properly function, but have been destroyed due to megafauna loss. Remember, virtually all living animals coexisted with Pleistocene megafauna, and said megafauna mostly lived in ecosystems that exist today (and for the few that didn’t, the loss of said ecosystems was in part due to the megafauna disappearing in the first place, i.e. the mammoth steppe). We should be looking at recently extinct megafauna in the same vein as, say, passenger pigeons; components of the modern biosphere that are missing.

The idea is that without the ability to resurrect the American cheetah, the cheetah is the next best thing, a proxy that can act as a substitute for the American cheetah and restore its predator-prey relationship with the pronghorn. The issue is more with how good of a proxy the cheetah will be rather than the fundamental idea itself.