It might be due to lack of time outside, namely to the decrease in exposure to sunlight.
Myopia isn’t an infectious disease, but it has reached nearly epidemic proportions in parts of Asia. In Taiwan, for example, the percentage of 7-year-old children suffering from nearsightedness increased from 5.8 percent in 1983 to 21 percent in 2000. An incredible 81 percent of Taiwanese 15-year-olds are myopic.
Common sense is helpful here. Looking at the sun is still a terrible idea, as is spending hours sunbathing. But reasonable time outside might be helpful for other reasons, such as vitamin D synthesis–evidently many people are likely deficient in vitamin D.