None of those services offer the same kind of content though. Tiktok offers 30s - a couple of minutes videos (vines, essentially), streams are hours long and are fundamentally different because they’re interactive with chat. YouTube offers the 5min - 30min edited content, with exceptions here and there (1hr+ content).
Your 11 year old nephew doesn’t watch YouTube because he’s 11 and has the attention span of a squirrel. He’s not watching a 30 minute video about the Canadian housing crisis.