This bit, at least, is easy to justify in D&D. This might just be my interpretation, but I'd rule that any injury that'd leave a person permanently disabled would require Regenerate or the like to heal. And that's pretty dang powerful magic.In a setting where you have magical/sci-fi healing why would anyone willingly decide to remain in a wheelchair?
It reminds me of the introduction to Seven Days to the Grave, a Pathfinder adventure that deals with an epidemic spreading through a city. And the question asked is, of course: how can that work with easy access to remove disease and similar magic (note: this was originally 3.5e and later remade as Pathfinder 1, so healing diseases was slightly harder than it is in 5e)? And the answer is that a city the size of Korvosa has like a dozen people capable of casting remove disease or the equivalent, which is nowhere near the amount needed to put a dent in the epidemic. It lets powerful people stay reasonably safe, but does nothing for the population at large.