Google has been anti yt-dlp before it was forked. They also have rules that carve out tools like this from their extension store and at Android, except enforcement is lacking sometimes.
Google is terrified of users having access users control to their video content.
Google's already tried taking down Invidious. If they could use the DMCA for it, I believe they would. Notable, Invidious is still up, and there were fun articles from the response
Weirdly enough, Google's never actually made a public statement that YouTube "has DRM". If they did, it would immediately give Kevin McLeod the biggest copyleft trolling opportunity in history, because all Creative Commons licenses specifically forbid using DRM on the resulting work.
The only reason why we even know YouTube "has DRM" is because third parties have been able to plausibly allege DMCA 1201 circumvention claims against yt-dlp regarding a nebulously named "rolling cipher". These are not actual court findings of fact, just that you can say this in a legal filing and not immediately get your case thrown out on summary judgment. Which is a really low bar. Whether or not the rolling cipher actually qualifies as DRM is still an open question.
The way DMCA 1201 is written, basically anything intended to function as copy protection is considered DRM under the law. Like, those really annoying no-right-click scripts people used to put on sites probably could be argued to be DRM under DMCA 1201. However, in this case, there's a disconnect between the people offering the DRM (who don't actually claim it's DRM) and the people using it as DRM.
Google has consistently maintained in legal proceedings and terms of service that its technical measures, specifically its "rolling cipher" and signature mechanisms, constitute technological protection measures under the DMCA.
The most prominent public declaration of this stance occurred during the legal battle over youtube-dl (basically the ancesor of yt-dlp). While the RIAA initiated the initial 2020 DMCA takedown, Google's own technical implementation of the "rolling cipher" was the core of the argument.
RIAA already tried to take down the Github repo for youtube-dl (basically the original yt-dlp was forked from) back in October 2020. But outcry from among others EFF got it reinstated just one month later. Google is probably on the fence about this because they saw how it went last time. The slow killing of adblockers in Chrome seems to be something they are getting away with, so maybe that will make them bolder once things have moved along far enough that there's no way back.
Because people download viruses from the internet all the time? "Common sense antivirus" might work fine if you're technically inclined, but that's not the case for everyone.
The growing prevalence of so-called "supply-chain attacks" (a bad name because it implies a commercial relationship that doesn't usually exist) shows that "common sense antivirus" isn't working so well even among the technically inclined.
Google is terrified of users having access users control to their video content.