I read an article about him back when the game was popular. He was making $14,000 per month off the game. He said he had no plans to quit his job. I guess the sales stopped and he stopped caring. But it's kind of weird not to care about something earning you $14,000 per month.
The sales stopped because the developer took the app from the store and made it really really hard to get thereby. He did it because he didn't want people to get addicted to phone games and contribute to that. So for him it was morals over money, literally! You can read about it on wikipedia
That's almost unheard of these days. I think it helps that he already had enough money, but still, a lot of people can never feel like they have enough money. Good for him!
Edit: holy shit! I just clicked the link. The game got to the point that it was making $50,000 per day! That's insane. $50k per day for something he coded over a weekend. Man, I wish the internet still held those types of opportunities for regular people.