I looked into this a while back and think it's been pretty well established that most autoimmune conditions are increasing significantly in the developed world and no cause is established.
Reading other (newspaper) articles it would seem that more blame is now being heaped on ultra-processed foods and there's a growing awareness that a healthy gut microbiome is key to good health. However, looking at other shoppers' trolley contents in the supermarket I can see that for the majority, these revelations are totally off their radar - little wonder we're getting problems!
It might just be mutational load due to people having kids much older.