Surely part of it is definition.
It used to be autism was a very, very rare disorder with children completely unable to communicate, etc.
Now they toss in everything from what was then known as mental retardation to almost any behavioral issue or unpopular personality quirk.
That said, debilitating issues do seem to have increased dramatically, whether primarily through vaccinations, environmental stuff, or whatever.
I have autism although it is very slight. In the old days before the Earth cooled, we simply learned to cope with it. We didn’t have computers or video games or fidget spinners to indulge the “beast” as I call it. My sole indulgence was reading, which I did all the time. If you indulge it with “push” technology like computers or video games, it gets worse. As I grow older, it gets worse. Luckily, I became a programmer so I don’t have to “adult” all day.
Autism(Aspergers) was probably common when I was growing up but we learned to keep it in check.