I want to open by saying: Look, I get it. I get why many people (particularly the native speakers of English, who are probably the majority of readers here) come to Japan and stay on.
After all, the incentives are so clear at the beginning. Right away, you were bedazzled by all the novelty, the differences, the services, the cleanliness, the safety and relative calm of a society so predicated on order. You might even have believed that people are governed by quaint and long-lamented things like “honor” and “duty.”
Not that the duties and sacrifices necessary to maintain this order necessarily applied to you as a non-Japanese (NJ). As an honored guest, you were excepted. If you went through the motions at work like everyone else, and clowned around for bonus points (after all, injecting genki into stuffy surroundings often seemed to be expected of you), you got paid enough to make rent plus party hearty (not to mention find many curious groupies to bed — if you happened to be male, that is).
Admit it: The majority of you stayed on because you were anesthetized by sex, booze, easy money and the freedom to live outside both the boxes you were brought up in and the boxes Japanese people slot themselves in.
But these incentives are front-loaded. For as a young, genki, even geeky person finding more fun here than anywhere ever, you basked in the flattery. For example, you only needed to say a few words in Japanese to be bathed in praise for your astounding language abilities! People treated you like some kind of celebrity, and you got away with so much.
Mind you, this does not last forever ...
Although there's truth in what Debito has written I think this applies to people pretty much everywhere and not just us long-term FG's. This is classic midlife crisis.