Yunno…it's funny you ask this question Jun, because I have personally known a few people that quit Aikido just before getting their black belts (1st and 2nd kyu) or just after they reached dan level because they felt if they stayed they would be obligated to teach and they didn't want to (they weren't done training yet).
This kind of falls in the "drop rates and reasons" thread, but it is an interesting phenomenon, and although it exists somewhat in Karate as well -- it is nowhere near as bad as in Aikido. It's interesting that students are expected to teach when they reach dan level in many dojos…something deserving of thought perhaps?
On the other hand I have seen a great number of inexperienced Aikido teachers. Maybe the two sides of the coin (the ones that leave before they "have" to teach when they know they aren't ready, and the ones that do teach even though they aren't ready) are telling us something?
Or not…just thinking out loud