> Something about Tiktok, whether the algorithm or the sheer volume of content, seems to discourage the sort of look-at-me envy-bait narcissistic posturing that is so common on Instagram.

I haven't used Tiktok, but from what I understand you can only post videos taken using the phone's camera and they can only be edited using whatever filters are available within the app, effectively limiting how manipulated or manufactured the content can be. Sort of like a Snapchat for videos (with the caveat that you can save and post videos at a later time in Tiktok, whereas with Snapchat it's "now or never"). Coupled with not having an associated text component where you can easily post testimonials and links to a site where you're selling a self help book, get rich quick scheme, juice cleanse or gym routine, it should limit how easy it is to use it as a promotion platform.