"Why Do Some Fairies Have Glasses"

My son asks an interesting question. Why do some of the fairies in the video he was watching have glasses? You'd think that, with all that vaunted magic of theirs, they could have magicked their nearsightedness away. In fact, there are many cases where you can ask why X, despite so much Y, still suffers from Z. The rich are still lonely, the powerful are still anxious, the famous are still insecure. Inconsistency bites, doesn't it?