I'm inclined to think the link in autism might be caused by the prevalence of C-section births not passing the proper gut microbiome to some kids who are also genetically more inclined to autism but only if the gut is screwed up at birth.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4464665/
Doctors nowadays do C-sections often for unnecessary reasons, such as expedience or shift changes or as a default because the believe its "safer":
https://opinionator.blogs.nytimes.com/2016/01/19/arsdarian-c...
The wrong micro-biome eventually builds up a toxic load that causes the onset of autistic symptoms. Most likely due to cell danger response (CDR) getting stuck:
https://health.ucsd.edu/news/releases/Pages/2017-05-26-centu...
Out on a limb, I know. But likely the cause is probably going to come down to a cascade of preventable events and toxic loads causing some kind of malfunction in those who are already gene compromised.