For me I think it's two factors:
1) Quick out if you don't like it. Load the next thing is really quick and easy to do. Just flick up and boom it's the next thing. Right now there are no ads or interruptions. It's really easy to move on from something you don't like.
2) The algorithm is really good. I don't know enough about it, but it consistently shows me stuff I want to see. I can't explain it more than that.
I also don't feel like it boxes me in the same way Youtube does. Youtube shows me nearly the same thing I have already seen and liked. Tiktok pulls up a good variety (sometimes from creators with single digit followers) that I am interested in.
You become like the lab rat hitting the lever over and over again to get a pleasure spike from the electrode wired to its brain.
I’ve found that my attention span and willpower have been decimated in the last few years. I can barely make it through a few pages of a book without reaching for my phone. I’m not sure if the (over)stimulation caused by apps like TikTok are the cause, but it seems plausible.
Incidentally, this is what HN upvotes on my comments are for me. I tried to abandon the use of smartphones entirely, but HN is the one addiction that I can't seem to kick. Even YouTube was easier to kick, and that one wasted a lot more of my time.