I have limited experience with PVP, only playing some in Galaxies and having tried all the types in World of Warcraft, maybe a tiny bit of Monster Play in LOTRO.
You don't have to write quests.
Maps are pretty limited in what they contain, right? World building isn't a big deal, and nobody cares how big your world is and if you can walk across it in a half hour.
You don't need many classes.
Armor and weapons can be your focus because everyone is looking for the next Big Bad.
Nobody has to think about too much about anything. You set things up, people go toe to toe. Somebody lives, somebody dies. Rinse, repeat.
You don't need lore.
Not really any need for writers, little need for artists. Cheap to run?