Genetics are the strongest factor. Your habits can contribute to your myopia.

I used to work a desk job and stare at a computer screen for 8 plus hours a day, always had corrective lenses since I was a kid. I switched careers to carpentry and left the computer monitor mostly behind.

I was at my yearly checkup and was noticing slightly blurry vision. Turns out my new profession made my eyes better. Over the years since the career change, I've gone from a -4.75 to a -4.0. Not cured by any means, but my habits changing made my vision better.

My optometrist had an interesting anecdote. When he initially asked me about the change in my career when my vision was getting better, he said that he noticed smokers would have more stable vision. In an office building, if you don't smoke you keep your head down looking at a monitor all day and your eyes decline even after genetics should've leveled your eyes off. If you smoke, you step outside every hour or so and look at the world around you, giving your eyes a rest.

One other take I've seen is you don't really notice eye strain from having imperfect vision if you're not sitting focused on a flat, non moving object all day (i.e. books and computers) so people who spend most of their lives not doing such don't notice.