I doubt it's the majority of watchers, but it is the majority of time watched.

I watch an occasional half our while eating, exclusively from my subscriptions feed.

But the kind of person who just watches whatever YouTube shovels at them -- they're watching for hours and hours on end, just letting the next video autoplay every time.

I don' think there are more braindead watchers -- it's just that the braindead watchers are the ones who watch the most.