I feel like the blue belts that quit after they get their blues are the guys that trained so hard to get their blue and can't imagine what it'll take to get to purple. Or the guys who treat jiu jitsu as just a hobby. The lifestyle jiu jitsu guys never quit.
I really don't understand how people plateau. There's way too much to learn and jiu jitsu is always evolving. I never once felt like I didn't progress after training. There's a bunch of ways to get better like drilling, rolling, stretching, cardio, strength and conditioning, dieting, watching instructionals ect... There's no reason to be plateauing unless you choose to like those guys that only bother learning what their instructors teach them, rather than constantly searching the web for answers to their own problems.
As for burning out, this isn't too much of an issue as long as you have a goal. If you have a goal, you can be burnt out and push through. I get burnt out every 3-4 months and I just keep training, business as usual and eventually that fire will spark again.