Perhaps this is the kind of attention he didn't want. His Twitter timeline makes him sound like a pretty humble indie dev who is more interested in making games fun than making money. I guess the "fun" part doesn't exist when you get death threats.

https://twitter.com/search?q=%40dongatory%20kill%20you&src=t... https://twitter.com/search?q=%40dongatory%20idiot

Probably has an inbox that looks similar.

If I had to guess:

He removed Flappy Bird from the App store so that the media would publish headlines like this, increasing attention focused to his app. Then, he has two options: republish, or sell. If he republishes his app, the media will publish another story, increasing downloads. If he chooses to sell the app, he can probably find a buyer in the dozens of offers he is presumably receiving right now (in between death threats of course).

Because he's an attention whore.