system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why didn't bad eyesight get naturally selected out?

A lot of people have awful eyesight that would make them almost useless in nature, and it's a high enough percentage of the population such that I don't think its survival can be attributed to the same reasons as, say, blindness being present. Did humans always have the ability to make corrective lenses, was it just not necessary for survival to have good eyesight, or is it something else?
gpt
The same reason that nothing existing today wasn't selected out.  Enough people with the "defect" were able to produce children that produced children.

There are various selective pressures that act on any specific trait.  20/20 vision seems to me to be only really important once we have printable type.  Before that, you only have to see a few important things to avoid death.  The main thing would be predators, which you could also detect with limited eyesight, smell, and sound.  Hunting requires only basic eyesight, because we don't hunt like hawks from high in the sky.  Gathering might require sharper eyesight for picking the edible food from the poison, or edible from simply non-edible, but not by too much.  And as previous post said, we evolved in social groups, so a bad eyesight person would do non-eyesight related things, while someone else picked up the slack.

If there were a sharp pressure on excellent vision deciding between life and death, it would have been weeded out.