Food and nutritional science is something many of us know (to a degree) and has been taught often in high schools. That is partly why you know that cheeseburgers aren't great for you, because you know they're highly processed, high in salt and high in fat and that's written on the label.
But the knowledge of the harmful impacts of social media aren't as abundant, nor are they identified or classified.
McDonalds are required to list the nutritional information of what you're consuming. TV shows and movies have content ratings to know what you're going to be consuming. Social media like Tiktok does not have any form of rating to know what you're consuming or going to consume.
There is a lot of less rigour on short from content like Tiktok, in comparison with McDonalds.