Or maybe not an increase in the numbers with the condition at all, but an increase in those diagnosed. People who were struggling a bit/a lot were just left to get in with it largely. Unless it was very obvious nobody got diagnosed in the past. Now the more subtle signs are noticed and acted upon by getting them referred for screening because people care about a child's MH.
Also because the high pressure environment of school, and to an extent home life, these days makes it more likely for the cracks to show before a person reaches adulthood. Primary school kids didn't have homework, at all, ever. Exams were non existent in primary school except the 11-plus just before you left and the results didn't matter much, you still went in to another school regardless.
Exams annually at end of year in secondary school and didn't mean anything either, until you got to GCSEs. Children don't leave school at 16 and get a job now. They're in education longer so more chance for things to be noticed. Parents didn't care as much, if you had a DC who didn't go to school you didn't get fined. Bunking off wasn't the end of the world. Neither was leaving with no exams. You'd still get a job. Not now.
And getting a job used to involve sending a CV to an advertisement in the paper or handing the CV into a shop or whatever. Not long complicated application forms. An interview was a brief chat to check you weren't a dickhead or if the job required some intelligence to check you weren't totally thick. Less hoops to jump through, less bullshit. Nobody asked daft questions like "why do you want to work for us" because employers knew and accepted it was because you wanted to earn a living.
You didn't have to justify your existence every year at the staff appraisal because they didn't exist. You weren't expected to constantly improve, study or move up the levels unless you wanted to. You were expected to turn up on time, do your job and collect your wages. That was it. Unless you were management, you never went to a "meeting".
If you weren't quite ok or didn't really fit in you could mostly still manage in something low-key. Not now. People cracking up left, right and centre, getting diagnosed as a result. Same for kids with school.