Because of the strict maintenance requirements on certified aircraft, you won't find many (read: basically zero) piston engine airplanes flying with improperly modified or defective mufflers. In single-engine airplanes, those could represent a significant safety hazard to the people in the cabin.

Turboprops and jet engines don't really have mufflers per-se. Some aircraft have aftermarket "hush kits", but that's relatively uncommon as well.

The one and only piston-powered airplane I've taken into a deep pre-buy inspection had a wrecked muffler core.

My sample size is one, so did I "win" the lottery? I have no particular reason to believe this aircraft is especially noteworthy for its airworthiness or level of care.