I think there's a combination of factors really.
Yes, society is more aware of mental health, the teens themselves are more aware. I remember feeling really miserable when I was in 6th form, but didn't have a name for it. I knew about depression, but didn't think it applied to me, it was what older people had.
Social media certainly plays a big part - they see so many fake images that convince them that's how others look/live/feel they start questioning their own lives. So many girls now believe they should have ridiculous eyebrows, or eyelashes so big you can't see the rest of their face, or be super skinny and wear designer clothes. My theory is if they can't be like those images , feelings of inadequacy set in.
But the worst thing for mental health recently has been the lockdowns. Teens & children were locked in their homes (some of which would have been abusive, or dangerous, or plain unhappy) at a time they should have been learning to socialise, go out into the world on their own, get jobs... They were even told to stay in their rooms, not even seeing their families!
My own kids were very different in how they experienced it all. The older one was fine (apart from doubts over exams) going out cycling and enjoying being without a care. The younger one had so much school work piled on (that was never marked), little contact with anyone apart from us, and became so miserable she developed an eating disorder. As did several of her peers. I didn't know this at the time, only recently discovered how many of my friends children developed similar problems. Some have 'recovered', some haven't and are still struggling massively.
I honestly think the teenage generation have been the worst affected of all. So I'm not surprised there's so much talk about mental health, sadly.