ELI5 Myopia - why can’t you buy myopia glasses off the shelf like reading glasses?

How common is myopia around the world? Is it caused by genetics or lifestyle? How has myopia evolved with human activities? In aAmerican drug stores you often see a wide variety of reading glasses. Why are there no pre made options for myopia or near sighted people?

... we explain like I'm five

Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: notofyourworld, forams__galorams, cultish_alibi, pearlsb4pigs, explosivelydehiscent, norrisn and queltis6000

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