There are a lot of girls with eye patches in anime, but how many are actually missing an eye instead of just sealing an ability like pic related?
>Draw a girl, call it a boy
Most people are right handed, and right eye dominant.
Going into what:
Said, about half these girls are just chuuni and not actually missing an eye. For that reason, they chose to cover their left eye since they are right eye dominant most likely. If they covered their right eye, it would be really difficult to navigate around and it'd just be way harder to live essentially. You might not think it makes a difference, but eye dominance does play a big role in eyesight.
For the rest, maybe it's just author preference. Maybe they're right eye dominant as well so they figure it'd be "nicer" to gouge out the character's left eye and save them some of the trouble. Or there might be a deeper cultural significance, I'm not sure.