They're an ad company at the end of the day; they still want their cut of the monetization.

Additionally both sides of the dispute normally still want the monetization, they just disagree about who gets the proceeds. And because of the time value curve of YouTube videos (most make something like 90% of their revenue in the first few days), demonetizing has a good chance fo essentially erasing the revenue of the video for the creator.

I mean, then YouTube is substantially cutting into their own revenue too, but even that would be better than just handing over all the revenue to an unverified 3rd party that clicked a button.