I think there are better ways of motivating players to keep playing than just by "having to play in order not to have thrown the subcription fee out the window".
Surely it isn't such a negative impact when the developers focus on making the game actually FUN TO PLAY rather than the consumer having to prove their "loyalty" to a product they've already paid for.
Besides, due to the game leaning in the sandbox direction, there isn't that much need for the development team to constantly keep up with user demand for content as time progresses. As the game's survival is supported by the players themselves, making -themselves- invested in the game and it's setting in their own way. This is a strategy which I think not only adds alot of depth without that much effort on the developers' side, but also cuts down on costs, thus lowering the need for subscription fees. It's a win-win situation as far as I can tell.
