I have searched and there are only hypothesis, mostly talk about how people read a lot and their eyes develop myopia but that also this could be because of people not getting enough outdoors time, there is even a chinese school whose students had a lower rate of myopia because they made their students spend outdoors time.
About 41.6 percent of Americans are nearsighted, up from 25 percent in 1971. “The trend appears to be upwards in many other parts of the world, but the changes have been nowhere near as spectacular as in East and Southeast Asia,”
Could this be because of the more rigorous study teams (with less outdoors time) of countries like China, Korea and Japan?. Some people say that race plays a role here too.
"In the developed countries of East and Southeast Asia, the prevalence has now reached 80 to 90 percent among children with 12 years of school. Projections suggest that almost 50 percent of the world will be myopic by 2050."
Half of the world?. It comes to no surprise too as urban life has huge benefits but also comes with the rise of diseases and illnessess that were almost non existent in the rural lifestyle (see depression, anxiety, cancer).
"Researchers are unsure why time outdoors helps prevent the onset of myopia. “One idea is that it’s just the amount of light to which children are exposed,”.
Like grasping in the darkness, as if you couldn't see. These are only theories of course but I find a lot of sources mentioning the outdoors time as crucial to the development of the eye.
Sources: