I think for a while, their strategy to ignore adblockers worked just fine. User counts were rising, ad payouts could be and would be cut, ads could be and would be placed in different parts of the video, videos that weren't monetized were getting ads thrown in just to make Youtube/Google/Adsense money. YT was pulling lots of levers to keep the value of advertising on the platform high.
That is, until Adpocalypse. My theory is, after this point, advertisers began to question how many more levers could be pulled until they addressed the elephant in the room, an elephant that was getting larger and larger: the adblockers. Let's be fair to Google (ugh), it would be much much easier to pull all those levers, than to tackle the technical challenge of stopping client-side software from running on their website. Once interest rates rose, and advertiser pressure reached it's current peak, Google started taking anti-adblocker actions: Manifest V3 to kill ublock on Chrome, Youtube's current system, etc.