Game companies have discovered that gamers don't like monthly subscriptions. Gamers accept the illusion of free to play, and patronize the in game stores because the think they are getting good value for their money.
It's a win win situation. Game companies get necessary revenue, and the majority of gamers get what they want, too. Cheap bastards like me play, but rarely shop.
I think there are still games that charge a monthly subscription. Eve Online comes to mind, but they also have plex and an online store.
Gamers have spoken, and this is what most gamers want.