They don't. They want to let people opt out of social media feeds for the same reason they currently let gamblers self-exclude[0].
Politicians do not believe that casinos are popular despite the gambling and they do not believe that social media is popular despite the feed. They want to protect the general public from addiction.
It's all fun and games when you download Tiktok. Then one day you're scrolling while your kid is in the pool, the lifeguard jumps in to save her, you realise you would have let your daughter die because you're addicted to watching dance videos on the fent rectangle, and you decide to quit.