I have my own theory. That is, that it's because of insulin. Let me explain. 90 years ago and back, if a person got type 1 diabetes, they died at a young age. Most before they were able to reproduce. So the gene for type 1 was less prevalent. Nowadays, if someone gets diabetes at a young age, insulin can keep them alive to a very old age. So, we are able to reproduce and pass on the type 1 gene. It's way more prevalent than it was in say 1910 or 1810 or 1710 etc.. It's sortof an anti survival of the fittest.
I have never seen any scientific articles suggest this explanation. So I may be way off. But it makes sense to me. As much as over cleanliness and vitamin D deficiency anyway.
I completely agree. It makes sense to me too. It's kinda along the lines of why Alzheimers is increasing. Back in the day, older people would die before they had a chance for Alzheimers to start. But now, with so many improved technologies, people are surviving to a much older age, and therefore developing Alzheimers.