I think the underrated thing is dopamine for new users. On pretty much every other social media you have to grind for months/years to see any huge numbers. On TT you can be a nobody, new account and post something that goes viral and have it seen by 100,000s people. If you scroll the For you page and see those vids then click on that user you will see their others videos often have 10x less views.
This initial dopamine kick for new users keeps them investing and wanting to create more content.
Also because you arent curating a page like IG people dont mind following 1000s of accounts the same way they do on IG