This is one of those situation where both things can be true at the same time.

Social media companies have shown that they do not give a shit about the mental health of their users, quite the opposite seems to be true. Yes, parents are responsible for teaching their children about the reality of modern social media, but they can only do so within the limits of their abilities and understanding. It's similar to smoking. Yes parents are responsible for teaching their children about the dangers of smoking and encourage them not to, but no one thinks removing the age restriction from tobacco is a sane idea.