My guess that is more likely to be microbiome or immune than internet use. This study just came out and could be relevant.
Hunter-gatherer lifestyle fosters thriving gut microbiome
A team of researchers has sequenced gut microbiomes from Hadza people — members of a hunter-gatherer society in northern Tanzania — and compared them with those from people in Nepal and California1. The study has found not only that the Hadza tend to have more gut microorganisms than people in the other groups, but that a Western lifestyle seems to diminish the diversity of gut populations.
The Hadza had an average of 730 species of gut microbe per person. The average Californian gut microbiome contained just 277 species, and the Nepali microbiomes fell in between. People with a farming-based lifestyle had an average of 436 microbe species, whereas those who live by foraging had an average of 317.
The team also found species in the Hadza microbiomes that were not present in the Californian samples, such as the corkscrew-shaped bacterium Treponema succinifaciens. Only some of the Nepali microbiomes contained this microbe, suggesting that the bacterium is dying out as societies become more industrialized.