i dont think its because of lack of players.
for example at the start of the game all players level are almost equal. Then when the game progress and there's player that leave the game we get high level players that will invade the game thus cause imbalance.
they should restrict this late comer's level when joining the game.

i've no problem fighting level 10 player when im just level 5 but when a level 25 player came with a +8 knife that can i slash me to death than thats a problem.

yes the game is fun and can be addicting, but this imbalance can cause frustration to the new players