Well, you’d lose support for devices which can’t handle software DRM playback, old YouTube clients installed on things like TVs which no longer get updated, if you want to support things that only get Widevine L3 support (most devices) you’re not really going to move the needle since Widevine L3 had been broken since like forever, etc.
The main thing YouTube would gain in practice from such a move would be to get DMCA as a legal tool to crack down on people ripping YouTube videos, but that’d require some very significant resources invested into driving Legal processes against average consumers ripping videos, and the return on investment for that is almost certainly abysmal.
EDIT: I thought of two more reasons:
Given the enormous scale of YouTube’s transcoding pipeline, just adding in a DRM step into the mix will cost non-significant amounts of money
All old content will remain non-DRM, because a re-transcode of the full YouTube catalog would cost an impossible amount of money
Well, you’d lose support for devices which can’t handle software DRM playback, old YouTube clients installed on things like TVs which no longer get updated, if you want to support things that only get Widevine L3 support (most devices) you’re not really going to move the needle since Widevine L3 had been broken since like forever, etc.
The main thing YouTube would gain in practice from such a move would be to get DMCA as a legal tool to crack down on people ripping YouTube videos, but that’d require some very significant resources invested into driving Legal processes against average consumers ripping videos, and the return on investment for that is almost certainly abysmal.
EDIT: I thought of two more reasons: