4. Boredom: Some people may just feel that they've learned "enough" to satisfy whatever their personal reasons were for starting to train. Maybe they feel like the progression in skill level as they approach blue is not as worthwhile as it once was when they were new.
All these replies and no one has thought of:
Maybe they don't like it!
I have been mulling on this point since the Blue Flu thread. Jag and some others brought up playing guitar. Would anyone begin to learn guitar theory, learn a few chords and scales, then just quit taking lessons, and playing guitar, forever?
Because lets be honest here, you stop going to a gym to train BJJ, it's not like you are going to keep those skills you've developed after a period of time, and how many of these guys are training on their own time?
At least without lessons you can pick up a guitar and strum out an old Neil Young song now and then to keep what small level of proficiency you deemed to be "enough" strong.
So what I'm saying is I don't think that boredom or satisfaction really has much to play into people quitting BJJ, unless they are holding the false belief that they will be able to retain everything they did learn forever.
And as far as the comments go about "These people are lazy, unmotivated and not dedicated" that is a very broad generalization.
They may be very motivated and passionate about some things. BJJ is not the end all be all. All of us here just happen to love grappling to the degree where we spend some of our free time on the internet posting in forums about it. So naturally it will irk us when someone says "I want to train BJJ so bad. Like so bad." But then not put any effort into it, or rather, not put into it the level of effort that we choose to put into it.
I'm gonna disagree a little here. If you think about how BJJ really progresses for most people, your first 6 months you see almost immediate improvements in your game as you build your fundamentals like upa mount escape, shrimping, basic positional control, and your core submissions. These things tend to be almost immediately applicable in their rolling and make the feeling of progress seem very rapid. Even the first year or possibly two, this is the case most of the time, because everything is "new". As you get further on and start focusing on honing skills in certain areas, this increases your effectiveness from those areas, but the progress seems to slow down for many people. You've learned the mechanics of the armbar and the triangle, but now you are focused on finding 10 different ways to get to the same armbar or half a dozen ways to get to the same triangle or choke. You may spend months refining your half-guard to a proficient level and so on and so on. Most of us understand the necessity of this and appreciate it for what it is. Others though may not share that enthusiasm. I've known quite a few that were this way. They aren't avid competitors and many felt that they knew enough to defend themselves if ever forced to and that their time and interest were drawn away from bjj to other endeavors. Maybe boredom is not the correct word. Maybe it is more a matter of disinterest.