You can't replace that just with an algorithm. These people have no alternative. That's why they've been actively rebelling.
TikTok is much better at surfacing interesting content. It fundamentally uses an interest graph over a social graph, which means at its core it cares much more about knowing what people are interested in than knowing to whom they're connected, which was the premise for older social media platforms. IG's "learning" seems to be a sort of auto regressive retargeting rabbit hole logic that just doesn't compare.
Yes, Meta(IG) and Google(Youtube) have the capability to develop this too, and have done it, but somehow manage to fuck it up consistently.
Aside from the technical features, the community on TikTok is completely different. You hit the nail on the head here. Have you seen the comment sections on the other two apps? TikTok has created a beautiful community, and it’s a community that cannot be reached by them, regardless of their feature set.