All the money in the world woudn't explain the popularity.
TikTok is, in a horrendous way, simply a very good product, because it is extremely addictive to it's target group.
I did some 'opposition research' and installed the app, and forcedmyself to doomscroll for an hour or so, after seeng a friend's kid doing it for hours on a vacation.
The constant, no-lag, no-buffering mini endorphine kicks it gives the user the "just ooooonneeee more" addiction. It's really nasty.
They also bombard you with click-baity notifications. Even though I didnt like or follow anyone, they seem to know that I am a middle-aged man, and I got notifcations of pretty girls doing borderline sensual things with clickbaity titles all the time.
I imagine they have the targetting down to a 'T' once they know more about you.
Facebook seems to be following suit - I researched some pregnancy stuff a couple of weeks ago, and for a while, my "Facebook Reels" (which I don't use. It's like Facebooks TikTok clone) was full of twenty-ish years old pregnant girls in crop-tops in a ton of make-up dancing and moving suggestively. I really really didn't like that, and thankfully the algorithm seems to have given up on showing me that right now.
But I recommend that everyone do the experiment of purposefully using TikTok/Reels/Youtube shorts for an hour or so. It really does things to your brain.
I personally think that these things are neurologically damaging, especially for kids. It's on a whole other level of endorphine mini machine gun that causes brain-dead addiction than the previous techs.
It's addictive in a similar way that wave surfing is. It's not that every wave you see is a great. It's the constant sine wave of expectation and dissapointments, with some cool gems in between that really screw with the brain. This is also why casinos are so dangerous to many people. And companies have diales in how to exploit that better than before.