As he wrote, he didn't put the game down because he was afraid of the money or didn't want to run a business, he was actually afraid of the effect the "addictiveness" of the game had on some of its users.

With that premise, selling to an established company would have been the most irresponsible thing he could do. After all, the biggest assets of the game are its large user base, the media hype and just that "addictiveness". So this would probably be the first thing any buyer would have exploited, making Dong's problem worse instead of better.