They really don’t. Some YouTube videos (and channels) are way more profitable for Google than others, on a CPM basis. I think there are even some videos that are just plain money losers (long videos that aren’t packed with mid rolls).
Google wants to steer you towards the most profitable videos and away from the unprofitable ones. They don’t care about your interests. They’d rather trick you into watching videos you don’t like and that get you angry (but keep you engaged) than to watch videos you’re really interested in but are too long and niche and unprofitable.