When I first began I had big dreams of getting popular and this and that. I think I realized over time that what's important about being a youtuber is simply being able to make a connection in a creative way. Promotion and demographics and what not can be thrilling if you start getting popular, but when that eclipses your desire to keep pushing yourself to try new things, have a real message, do something unique and out there, impress yourself and your audience, that's when channels tend to get more generic, boring, and sometimes even annoying. I've seen alot of people who promote promote promote, and when you watch their content it's like they just make it to have something to promote.
I think some people are perfectly happy with just that, they keep doing the same thing, churning out video after video, and watching their popularity rise because maybe they're just good looking, or maybe they've found a niche that a certain crowd wants to keep viewing, and when a person has that sort of luck, I can see why they'd want to keep going. But it also seems like a way to wind up fizzling out, because gimmicks usually have a shelf life, and no matter how much people love something if they keep getting it they will probably get bored with it at some point. So if you're not sitting on that firm foundation of a desire to connect, and keep yourself as entertained as your audience, you'll probably fizzle out at some point. If not by losing your audience, by just feeling bored with your own content.