The study they linked is just self reported data from an internet survey. I'm sure that 13 year olds who don't get enough sleep because they're endlessly scrolling through ads, influencers, and disinformation don't see any problem with it the same way that a survey of alcoholics will show that beer is great, alcohol improves their lives, and that of course they can quit any time they want.
I'm not even suggesting that this ban will be effective or helpful, or that such bans are a good thing, but we know that these platforms are used to prey on their users, that "negative experiences" can be found easily, and that there's actual evidence of actual harms caused or facilitated by social media (including corpses). It should take a lot more than the opinions of just over a thousand children to discredit all of that and cause us to assume there's no problems with these platforms, how they're being used, or the effects they have on children.