Which sites?
Tumblr was started in 2007 - it wasn't very big until 2009. I'm not sure why it's even in your comparison.
The only company worth hundreds of billions of dollars remotely relevant is Facebook and - possibly - TikTok. Are you implying that the majority of their business is promoting teen mental illness and eating disorders? Because it's not - especially Facebook. Most of the tweens have moved to TikTok.
Facebook's audience is like ~3% teens & tweens. And of that a small percentage is getting sucked into this strange & toxic echo chamber.
The reason this is mostly a TikTok problem is because Facebook can easily and did do things to prevent this. They could do more, and TikTok can certainly afford to do something about it. The impacts on the top and bottom line would be irrelevant.
I'll end by saying I find it odd we seem to be talking about this being a children only problem. Every time there's a new allergy in the buzz or a new condition - I have at least 100 contacts talking about how they're convinced they have it. This is just typical human behavior - trying to always be the center of attention. Should we be surprised kids want to special? No.