I wonder how much revenue these channels would produce if comments were universally disabled.

Nearly every popular YouTube video is its own discussion board. There are people discussing the video, other comments, and completely unrelated topics. You see comments like "Hey, I'm back. How are you guys doing?" -- which implies this is a person who treats the video as its own self-contained forum.

Then of course there's the trolls who perpetuate conversation by inciting others. It's ironic to think trolls earn video channels ad revenue.

Yeah, most of the internet hasn't heard of a hosts file or AdBlock. It's a good thing though, because if there wasn't money in the advertising we would have to pay for access to YouTube.