The world classification exists as a tool to balance world populations. They want players to be creating new characters on worlds with lower populations and avoiding those worlds with high populations. As a world's population shifts to one or the other extreme, they'll change the classification.

Considering NA players tend to demand high population servers to play on, don't expect SE to add any more NA worlds unless all NA server populations are getting close to what the servers can handle. And expect the highest population worlds to remain marked as congested.

Quote Originally Posted by Derby_Crash View Post
The servers probably wouldn't be so congested if Square actually got off their bums and bothered to deal with the amount of bots...
Fun Fact - a bot operator can't create new characters on congested worlds any more than actual players can. If bots were the true cause of congestion, congested worlds would very quickly lose their congested status as the existing bots get banned (see the weekly notice).