There are, I still think, two types of cosmetics: type one is naturally occurring and type two is something you’ve clearly done to yourself.
Cosmetic surgery, meanwhile, is obviously type one. No one’s going to say “Nice surgery”. It’s not a sign of taste and self-respect to have gone under general anaesthetic and been selectively carved to reverse what our culture considers to be the uglifying effects of getting older. It’s supposed to look like nothing has happened, even though it’s often obvious something has. So it’s rude to mention.
People who get facelifts just want to look like they haven’t aged.