That's the power of positive and negative reinforcement. They want to shape the behavior of players. They want players logging into the game multiple times a day, every single day.
So they rate limit the player's game with "stamina" or whatever euphemism for a timer they come up with. Player was having fun playing the RPG with friends, only to run out of "stamina"! The choice is to stop and wait for the timer to reset or pay money to reset it. Then the player starts waking up at 3 in the morning because that's when the timer resets.
The simple timer reinforces a schedule and creates the behavior the game developer wants players to have.
This is a common technique for manufacturing commitment: if a person must suffer for a thing, they come to justify to themselves that the thing is worth the suffering, and become more dedicated the more they do. Cults often use this technique.
But I've seen so many similar games where the game itself wasn't fun at all, even though the rewards were still enticing. The Simpsons Tapped Out comes to mind. And in those cases I realized the game play itself wasn't interesting or fun and quickly quit. Basically, any game that has timers in it will fall into this category because the timers are there solely to make sure you keep coming back and have a compelling reason to do it often.
In the old days, the focus was on playability. Games were fun. But a new genre has emerged particularly in mobile gaming that does something strange: it compels play even when it isn't fun anymore. In the old days when a game stopped being fun, you would stop playing. But these games, when they stop being fun, you make an in-game purchase...