These are 2 possible ways to attract players, events and a balanced game.
Events: Sure, everyone loves to have an event in the game. Who wouldn't? But think about it. Events only last days or weeks, depending on how big it is. Also, it requires extra work from staff to plan out and to decide what event should it be, what pokemon should be available, what's the prize for the event, and so on. Event's are not long term, but it pulls in more players to play the game because events are give players a thrill of adventure and excitement.
A balanced game: With the variety of available free MMO games available, what stands out the most are those that are well-balanced and crash less often compared to other MMO games. A game is balanced as long the staff focuses on balancing the game on how it's supposed to be laid out and built. Updates may come once in a while to improve the game, but the main priority is to balance the game to lessen crashes and bugs. These are long term, but it pulls in less players compared to events.
I've laid out the 2 possible ways to look at this. You guys decide ;D