Why do so many people wear gles?

Okay this is kinda simplified, but let's say Bob a sapien sapien that lived 20,000 years ago (random number) didn't see so well. Well poor Bob walked off the edge of a cliff, Bob did this before he had offspring. Well if Bob had lived today he would have gles or contacts or whatever and he would avoid the cliff, so Bob would live long enough to reproduce. The Bob of today gets to p on his faulty genes and make little Bobs and Bobettes who can't see either. The Bob of yesteryear didn't get that chance. Long story short, gles help from an evolutionary standpoint because technology has compensated for a trait that should be naturally selected (do you get what I mean?) out and now "visionally challenged" (made that phrase up) people like Bob get to have kids.