Google has a ton of interaction data to be sure, but the app design decisions of TikTok (auto play, auto loop, easy swipe, easy like, etc.) extract so much more usable/actionable interaction data. The size of the like button on YouTube is a tiny percent of the screen. On TikTok the like button is the whole video.
Not just that. The whole UI is designed for behavioral data aggregation.
It’s not just “did you click the like button”. It’s “did you swipe it away? How long did you watch until you swiped it away? Did you come back afterwards? Did you let it loop multiple times before moving on?”.
They’ll capture likes and dislikes you yourself probably didn’t even knew you had, just from tens and hundreds of these micro actions. And they’ll do it in the very first hour of you using the app, whereas YouTube won’t know too much about you even after months of you using it.
