Question about possible reasons for why my dentist can’t remove wisdom teeth?

So I’m just curious about something. Not looking for a diagnosis or anything. But basically, a few years ago I went to the dentist and they told me I had impacted wisdom teeth on the bottom. They easily got infected until I learned how to clean them extra efficiently. When I got the X ray, my dentist said that he could not remove the teeth even though they are causing issues, because “there is a 50% chance it could paralyze my face.” What are the possible reasons for that? And is this kind of thing common? He didn’t really explain and I’ve always been curious about the possibilities