That's not 100% true. It's only really the case in patent protected medicines.
New drugs undergo testing, to get FDA approval. New surgical treatments don't. New (and old) surgical treatments and old drugs aren't lucrative enough to warrant real testing. Surgeons will claim it's for ethical reasons, or because they just know better, or that they are artists who can't be constrained by the laws of statistics, but it's simply a lack of regulations and / or incentives.
New drugs undergo testing, to get FDA approval. New surgical treatments don't. New (and old) surgical treatments and old drugs aren't lucrative enough to warrant real testing. Surgeons will claim it's for ethical reasons, or because they just know better, or that they are artists who can't be constrained by the laws of statistics, but it's simply a lack of regulations and / or incentives.