It's not that people can't learn something from youtube, but that's not where most of people (not just the children) are spending most of the time. Just because someone watches a few videos about something useful to them that doesn't mean they aren't also being exposed to things that are harmful to them.

There are a lot of benefits to social media, and it could be a positive thing with fewer downsides, but there are basically no regulations to stop platforms from exploiting and harming children. The industry also refuses to regulate itself and prevent harms (many of which they created/cause in the first place). Parents clearly need to do a better job protecting their kids, but I have to admit that it's difficult when their children are being targeted and manipulated by companies with trillions of dollars while parents have to spend most of their time working just to keep their kids housed and fed.