It differentiates them from "consumers" who watch the videos. When you have two different groups of users you need two words.

Also, I think you underestimate how much work goes in to some popular channels. People with millions of subscribers often have production teams that would rival a well funded TV show. It's something I find a little saddening when kids say they want to be a YouTuber as a career choice; they think it's a guy in his bedroom with a camera and a laptop. It really isn't.