Because social media is precisely in the short term benefit x long term risk that human brains are bad at conceptualizing. Same reasons for why we mandate belts in cars.
Hardly anyone in the "west" gets pulled over by police for seat belt checks (unlike say, India, China), yet nearly everyone still wears them, because they understand if they don't, they'll probably become a stain on the asphalt. I imagine if tomorrow, a law passed that seat belts no longer had to be worn, most people would still use them. Perhaps the regulation and enforcement are only needed initially when not everyone is educated on the long term risks.