Ads obviously, and people that pay YouTube premium also contributed to monetization but idk how much

It's the exposure, which leads to more ad revenue (in theory, without adblockers). YouTube creators live or die based on the algorithm and two of the main things the algorithm looks at is frequency of posting and engagement. Since Google needs metrics to give advertisers some idea of revenue potential, someone liking your video isn't nearly as valuable to the algorithm as someone liking, commenting and subscribing (if not already subscribed obvi). As an example, ElectroBOOM just started making shorts of all his old content because he's in the middle of a big house move and doesnt have time to make regular content which he noticed led the algo to stop recommending his content as much. But as far as just making a junk account and liking every video Google has systems in place to ignore "stale" accounts that don't actually watch the videos. Ultimately what they want is viewers since eyeballs equals ads equals revenue and everything else is just a way of predicting future views.