I think it's funny that the majority of causes you list (isolation, not enough physical activity, little vitamin D/Sun exposure) wouldn't apply at all to the group you cite as having widespread issues (girls HS volleyball team).
As someone who struggles with mental health issues, and frequently not getting enough of many of those things mentioned, I've worked to try to do better about some of that; and it can sometimes help a bit. But the whole "get more exercise, touch grass, see a friend" isn't the magic cure-all that some people make it out to be; and worrying about doing enough of it can become a stressor all on its own. Additionally, seeing them as the solution can sometimes lead to harmful obsessive behaviors of trying too hard to seek them out, at the expense of other things like work or family time.
Anyhow, not saying that getting more of these things is bad, or that they have no effect. Just that a lot of times discussions of mental health online feel very reductive. More exercise, more outdoor time, more time with friends, more antidepressants; each of these could potentially have positive effects, but they can also have negative effects, or be unobtainable, or there could be one of myriad other issues that need to be addressed, or there could be situations, either mental, physical, or social that are so broken that they can never really be addressed, just lived with or in some cases not even that.
I think for people under 30, reducing social media exposure would help a lot (in general, for all ages - but many of those under 30 seem to live and breathe social media esp. girls/women)
As someone who struggles with mental health issues, and frequently not getting enough of many of those things mentioned, I've worked to try to do better about some of that; and it can sometimes help a bit. But the whole "get more exercise, touch grass, see a friend" isn't the magic cure-all that some people make it out to be; and worrying about doing enough of it can become a stressor all on its own. Additionally, seeing them as the solution can sometimes lead to harmful obsessive behaviors of trying too hard to seek them out, at the expense of other things like work or family time.
Anyhow, not saying that getting more of these things is bad, or that they have no effect. Just that a lot of times discussions of mental health online feel very reductive. More exercise, more outdoor time, more time with friends, more antidepressants; each of these could potentially have positive effects, but they can also have negative effects, or be unobtainable, or there could be one of myriad other issues that need to be addressed, or there could be situations, either mental, physical, or social that are so broken that they can never really be addressed, just lived with or in some cases not even that.