i bet i know what the guys is quitting...he's lost his passion for music. it happens to most people at some point...and then you can either quit or keep going without really caring that much. quitting is not necessarily the worst of those options either. if you're not that into it anymore, let others who are take the reins and go find something else you can be more passionate about.

the "music doesn't mean as much as it once did" bit is a most likely a rationalization.