Some logical thoughts
I've registered to post on the macrumors forum just to respond to this post, because there's so many crazy thoughts here that I felt strongly about responding to. I think many people on the forums are looking at this through their own tinted goggles, and may not see some of the realities that the rest of the world goes through.
First, some argue that money is most important, and the developer was stupid to let it go. On the other hand, many argue that the American values of getting rich are shallow and privacy are much better valued. No one really thought about what are the possible values that the developer may be operating under. My own understanding is that in certain Asian countries, yes money and fame are very much valued, and privacy is not valued as much. And I think Vietnam is one of those countries. Both privacy and charity are mostly western values and not as common in most Asian countries, so I'm sure Nguyen was happy to have it to begin with.
However, we should also look at the realities of a country where there still exist a large fraction of the population who is still very poor. He is not living in Silicon Valley in a gated community. It's most likely not as simple as just changing his email and social media handles and getting off the Internet. Most posters in this forum simply don't understand the crime situation outside their protected neighborhoods, especially organized crime. Many countries have bigger forces at work such as triads or massively organized gangs who keep an eye out on who's doing well lately, and can easily "persuade" you to do things. "Attention" might not just be threats on Twitter, and instead be actual knocking on his door from triads wanting a piece of the cake.
That's my guess as to what "attention" he was getting. Given the choice of giving up a large sum of money, or having that money but living in fear of endangering the lives of yourself and your loved ones, the choice is pretty clear. In that case it would be beneficial to him to publicly declare that he's giving up on the app, so that those around him would know as well he's no longer as successful.
There's no way to know for sure at the moment, but my guess is that he enjoyed making money, but bigger forces were at work to force him to give up that money, that being either greed or jealousy from organized crime groups being one possibility.
In many countries that's the reality of life. You want to be very successful so you can live well, but not too successful to attract unwanted attention that can endanger you and your family.