While Youtube may be discounting direct revenue from this specific and limited set of content, Alphabet recognises the value of ostensibly being the quasi-exclusive repository & catalogue of video content.
Denying to their "users"/viewers the availability of some subset of content hurts their reputation more than "losing" a negligeable fraction of direct monetisation.
Leaving aside the morality of repudiating monetisation while allowing access, this is a sound strategy for maintaining the Youtube platform's monopoly and raison d'être. Which is after all the core of their ability to maximise shareholder value, and what else matters to a corporation?
Especially if This Time(tm) we manage to get an open alternative running well enough for public use. I know I'm definitely going to look into ActivityPub for my social circle, and DDG is more and more credible. There's yet hope I guess!
https://github.com/alicevision/AliceVision https://github.com/alicevision/Meshroom
No affiliation, just an excellent tool