How does the rate of hospitalizations prove anything? Perhaps a growing awareness of mental health made people who were eligibile for hospitalization seek medical care, whereas before they would not be hospitalized for lack of a diagnosis? Or perhaps the same awareness made teens enact the pathological behavior they learned about online, complete with self-harm and suicide atemtps?
Any measure you can think to track a condition that is defined, diagnosed and (especially) self-diagnosed subjectively, is by definition subjective.
Then you could just look at emergency admissions where the patients were brought in after self-harm attempts that left them obviously in need of immediate medical attention. Unless you're going to suggest our standards for judging whether someone might bleed to death (for example) have changed noticeably in recent decades.
Seems to me the idea that teens today are no different to those of prior generations, we're just better at noticing when they've self-harmed (or indeed, committed suicide) and more likely to attribute that to mental health issues is at best wishful thinking, and at worst dangerously dismissive.
This unassailable conviction that everything can always be chalked up to "more diagnosis" for every mental health trend is a thought terminating cliche. What can't be explained away by "oh, it's because diagnosis is easier and/or people are more open about their problems", regardless of whether that's the primary cause?
Any measure you can think to track a condition that is defined, diagnosed and (especially) self-diagnosed subjectively, is by definition subjective.