Growing up natively with social media seems like a very reasonable correlation for me. Your life and habits are always under a lens, self consciousness or conscientiousness make sense.
I expect lots of formal study of these phenomena in coming years. As a parent of kids 7, 13, and 16 who spends a fair bit of time around school campuses & youth sports teams, for all the whining and complaining adults do about young people, my experience is that today's youth are by far the most empathetic, compassionate and best adjusted yet. They're going to be ok (provided we can afford to educate them and then hire them into the working world).
I'm not on TikTok and generally try to avoid a lot of social media, so the uptick in gym rat lifestyle is not something I've been aware of. Certainly a good thing though and it's nice to see a whole generation not submitting themselves to permanently being on weightloss hormones or chronically obese. I'm in my mid-30s and folks in my social circle are either fit with quality fitness interlaced into their weeks or above average in weight. There's rarely an outlier from those two groups.
When I was in high school ... nobody went to the gym. There weren't many gyms around, now there are a lot.
I do worry though that it might be cost prohibitive or even just limited to some social groups.
Modern gyms can be surprisingly cheap.
Gone are the days of the 1980s when the only option was $$$ for a 'health club' with squash courts and swimming pools, stuck in a year-long contract whether you went or not.
There has been a rise in 'low cost gyms' which are less of a glamorous club, and more of a warehouse with a load of free weights, treadmills and stationary bikes. Often there's barely an employee in sight. In a lot of places $25/month can get you 24-hour access - with no joining fees, and you can cancel whenever you like.
Of course it's still not as cheap as sports like running. But just because someone goes to the gym, doesn't mean they're paying $250/month.
Lifting has definitely played a changing role in my life. As a kid it definitely did instill the idea of working for results. It was extremely rewarding to see that when I worked out consistently and with a plan, I was stronger than my friends who went inconsistently or with poorly planned workouts. As an adult now it's more therapeutic - so much of my day is ambiguous, out of my control, or searching for how to apply my leverage instead of actually just applying my leverage. So it's very nice to have an hour of my day where I decide what I am working towards, and be able to hit clear goals largely by putting in blind effort.