The devil is in the details with these games. They need to balance a complex system of interactions, features, economies. They have to adhere to "easy to learn,

The devil is in the details with these games. They need to balance a complex system of interactions, features, economies. They have to adhere to "easy to learn, hard to master", to remain accessible and reward active players at the same time. They are also genres with a ton of competition and only the most engaging and well designed come out on top. I would say those things are all hard.