If they shut down yt-dlp for good, a lot of power users and creators would find the YouTube platform useless for themselves and abandon it en masse for its nearest competitor. A tool like yt-dlp is very much required if you want to engage professionally with that kind of community. Even something as trivial as making a well-produced "video reaction" relies on it.
Yes, YT has good monetization, but it still pays peanuts to the average creator. So the competitive threat is very real - superstars alone wouldn't be enough to make for a really compelling platform.