Let's watch together starts to fall flat when the primary use they have for a device is to chat with family and friends, where it's natural to want a modicum of privacy. I wanna know who they're talking to, not everything they say.

Then, they start watching what their friends share in group chats. I can mostly avoid social media doom scrolling by preventing them having accounts, but not so YouTube.

And it's a tough decision to blanket ban YouTube, since it is used for educational purposes, including by teachers (a teacher wouldn't point a 13 yo pupil to TikTok).

YouTube didn't need to compete with TikTok or Reels; they chose to.