It was always autism, but the definition was very narrow. The classic definition, iirc, is the cases where the person is basically wholly non responsive. Those cases are pretty rare. The new definitions has expanded in all kinds of directions, thus adopting more and more cases.
Until the Feds began providing school $$$ for autism, it was very rare indeed, because it was defined very narrowly. I had acquaintances in the late 60s with a son who really WAS autistic - completely incapable of any human contact, non verbal, fixated on machinery and loud noises, just sat around and rocked repetitively. When they became too old to care for him he had to be institutionalized. Horrible, horrible situation but there was literally no way to make contact.
Now, kids who are just "a little odd" are given a diagnosis. It's made it difficult to quantify the problem, or to get any kind of strategy going to help the kids who really have the disorder.
Nope. Wrong.
While there is some truth to what you say, that some kids who might have been called ADHD 10 years ago might be given a spectrum dx, you need only to spend time in a preschool to understand that things have changed dramatically since the 1950s-1970s. There is rarely a group of 25 kids without one or more children in it who pay no attention to what is going on around them, and don’t seem to be able to do anything about it. No eye contact, sometimes very limited speech. These are the undiagnosed kids at 3, not the ones who earlier clearly had something wrong, because those kids don’t end up in typical preschools. The more highly functioning often have new parents who just don’t want to believe it. Often their kids are bright, and can read, can play games, etc. They just don’t know how different their child is until he is with a dozen or so other children, and then his lack of ability to be part of the class becomes disturbingly clear to them.
In my child’s class there are two. One is sweet and shy and no trouble in the class, but all he wants to do is open and shut doors and gates. He will sit quietly but if given a chance will go to a door and begin his thing. The other had to get an aide because he was unable to sit quietly and unable to take any direction. He yells, he takes toy cars and perseverates over spinning their wheels, he gets too close to other kids and touches them like they are objects.
Talk to older teachers who have been teaching for thirty years. They will tell you. It’s an epidemic. SOMETHING in our environment is causing this.