What I don't understand is why aren't these companies suing YouTube/Alphabet?

They're the one's enabling the purported copyright violations. They're the ones profiting. They're the ones with the mountain of money attorneys are generally employed to take from.

If anything these attorneys should be supporting youtube-dl/yt-dlp maintenance and using it in support of their claims. What could be more damming of YouTube's negligence than showing the court a silly headless web browser written in python optimized for video sites can leech copyrighted materials from youtube.com?

YouTube/Alphabet will only get off their asses and _really_ prevent this activity the moment it costs more than the neglect generates in revenue.

Maybe this is some 4D chess, but from where I'm sitting these attorneys look like clowns.