If it is the case that incidence is notably higher in people with impaired vision, and it is the case that in pre-modern societies impaired vision was far more common, then that would seem to provide a plausible explanation for why so many more otherwise rational people saw supernatural events in pre-modern societies than societies with access to better medicine.
Contrast the alternative hypothesis: people in pre-modern societies were all gullible and stupid.
If it is the case that incidence is notably higher in people with impaired vision, and it is the case that in pre-modern societies impaired vision was far more common, then that would seem to provide a plausible explanation for why so many more otherwise rational people saw supernatural events in pre-modern societies than societies with access to better medicine.
Contrast the alternative hypothesis: people in pre-modern societies were all gullible and stupid.