It's sad the second the prospect of rewards was taken away we lost about 90% of the community.... Thought that's as least partially due to how long it took for the replacement site to come up with absolutely nothing inbetween.
I stayed still after the rewards were gone. When the forums came up, I didn't really want to stay since I hate forums because everytime I try to voice my opinion, I get shot down and someone tries to start something with me X_X
The community began to defeat its purpose. The point was to get the word out to others to buy the games. The missions reflected that. Then the un4 fiasco happened. I remembered when people were posting on here "Wait till un5, skip un4, they have to release un5" not knowing due to the ps3 coming or being out each games was on a sales basis. Un4 sales weren't good so the US didn't get UN5 though Europe did.
Why continue a site that was starting to hurt sales. Granted other sites like Gfaqs did this but Namco doesn't run Gfaqs. Also, the main games aren't yearly releases and no one hardly pays attention to the handheld games. The incentive(increased sales) to keep up this site was gone. They were just gonna close it completely but apparently there was a movement among the forum goers to keep the forums at least. It took a while and people moved to other sites.
Personally I think what really killed activity was how long it took to transition to this site once Hokage's room closed down. There was no site for months and we lost a lot of people in the process.