This is certainly more appropriate for /r/askanthropology, but I can provide a brief response here. First of all, this would require myopia to be hereditary. While it definitely is linked to inherited factors, there are definitely other factors that can lead to poor eyesight. But even if we assume it's entirely hereditary and take away eyeglasses, neasightedness would not be selected against, in most communities. Myopia is not enough to prevent someone from reaching reproductive, from producing fertile offspring, or (theoretically) from finding a sexual partner. Most of us live in a substantially stable society that a small factor like myopia would not be rapidly selected against.