You conveniently side-stepped the argument that YouTube already knows how to serve DRM-ized videos, and it's widely deployed in its Movies & TV offering, available on the web and other clients. They chose not to escalate on all videos, probably for multiple reasons. It's credible that one reason could be that it wants the downloaders to keep working; they wouldn't want those to suddenly gain the ability to download DRM-ized videos (software that does this exist but it's not as well maintained and circulated).
It seems more credible to me that they would cut off a sizable portion of their viewers by forcing widevine DRM.
Or is it something different you are thinking about?
What benefits does DRM even provide for public, ad-supported content that you don't need to log for in order to watch it?
Does DRM cryptography offer solutions against ad blocking, or downloading videos you have legitimate access to?
Sorry that I'm too lazy to research this, but I'd appreciate if you elaborate more on this.
And also, I think they're playing the long game and will be fine to put up a login wall and aggressively block scraping and also force ID. Like Instagram.
Would be glad if I'm wrong, but I don't think so. They just haven't reached a sufficient level of monopolization for this and at the same time, the number of people watching YouTube without at least being logged in is probably already dwindling.
So they're not waiting anymore to be profitable, they already are, through ads and data collection.
But they have plenty of headroom left to truly start boiling the frog, and become a closed platform.