I guess that at some point at blue belt, everyone hits a significant plateau, and will ask themselves honestly what are they aiming for, why should they keep walking through that door given that they are not getting better. At that point, everybody has to find a personal, yet very strong reason for training, or they will quit. My personal reason might not be good enough for you.
For me, there are two reasons that motivate me 1. Jiu-jitsu is worth sharing and 2. I can't think of a more useful and fun form of work-out.
Jiu-jitsu is worth sharing, means that there is always something to be learned, and that brings people together. The art is that good. It puts everyone on the same level : everyone is a student, exchanging techniques ! It just feels right. BJJ doesn't belong to any one individual or group. It's a living thing : it grows and evolves with every sparring match, formal class or informal discussion.
We all know we have to work out. Our physical bodies demand it. As a species, we are inherently competitive, aggressive people. We're hunters gatherers at heart. I think safe martial arts with a live sparring component, can and should be practiced for long periods of time without any major injuries. I can think of Judo and BJJ as examples. Not only do I get a damn good workout, but I also learn self-defense, know my body, build networks, etc.