Another plausible reason that I've not seen reported is that if he was indeed pulling in $50k/day, that makes you a target in Vietnam (average monthly salary $185). In that part of the world, being rich without having the right connections/protection can be very, very dangerous.
Do you have a source for this? I've only heard this said on HN and I doubt that it is significantly dangerous to be rich.
Let me put it this way. You are poor. Your family is poor. Everyone around you is poor. When you are financially in trouble, you ask someone to lend you money. In Asian culture, you don't start asking bank for money. You ask your friends, relatives and neighbors for help.
Now you are famous. Making $50,000 a day. Everyone is going to come after you and ask for help. You don't want to because who wants to be debt collector? But you have to because they are your relatives, friends and neighbors. You are in a dilemma and you don't know what to do about it.
Also, regardless of where you live, when you are rich you and your family becomes kidnappers' target. In countries like Vietnam making $50,000 a day makes you a millionaire to the people who are just making a few dollars a day...
He was happy with the initial revenue but he then realize his publicity would have cost him relationship with other people and that's what money can't undo for him. He just can't.