I think that's probably exactly it. I don't know whether the ad ratio is different, but you're just far more likely to see something new and interesting on TikTok vs scroll pass mountains of uninteresting or meh things until something comes along. I dunno in terms of where you'd see more ads and who knows you probably do see more ads in the low-reward boring app that you have to scroll forever on. But when your thumb is hovering between launching two apps, it's not rocket science where it's going to learn to land.

And I agree with the other commenter that TikTok is good at finding novelty in ways the other is not. Things like YouTube or whatever will just show you endless variations of the things you've already liked. TikTok will throw you things you like from way out of left field.