From my admittedly completely uninformed position, this looks so much like academics searching for some profound insight that will win a Nobel prize (or perhaps just guarantee a tasty stream of research grants) when in reality the truth could be much simpler. Let's look at an example of a group that suffers disproportionately:

'The high level of schizophrenia in black Caribbeans living in the UK probably reflects the interaction of multiple risk factors, many of which cluster in the black Caribbean community in the UK. Particularly significant factors appear to be the combination of isolation and exclusion, both within society (living in areas of low ethnic density and reduced participation in society) and within the family (family break-up and paternal separation). These factors seem to be more powerful than socioeconomic disadvantage, which is more likely to be a consequence than causal. Racism itself may contribute to social exclusion, increasing the vulnerability to schizophrenia. Biological or genetic susceptibility do not appear to explain high rates of schizophrenia in black Caribbeans. More research is needed about the role of cannabis, particularly in its more potent forms, and whether this contributes to the excess of schizophrenia in black Caribbeans.'

Perhaps it's as simple as: people that are born blind are to some extent insulated from risk factors that are conducive of schizophrenia.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2418996/ (just the first article I could pull up on a phenomenon I was aware of)