Im a university student training to enter medical school or chiropractic, and i was wondering how the hell people can regain most function from a severed nerve (laceration or crush injury) like from a knife wound, but many people on here struggle to regain normal function from diabetes or another illness with their nerves fully intact.

I've been studying nerve injuries (neuropraxia, axonotmesis and neurotmesis), and most people with a neurotmesis injury (most severe, aka a full severing of the nerve) can restore 50-90% of original function, thats with all layers and blood vessels of the nerve completely damaged. So how can people on here be suffering from nerve damage for so long when their nerves are fully intact with all axons and supporting layers in their original layout?