Tippa over at West Karana said something I've tried to articulate for awhile. And she said it much better!
Inertia is the inclination of moving objects to keep moving, and for stationary objects to stay put. Once you get going in EVE, it’s easy to keep going. The skill queue charts your course, you have your market ops and your research and the ongoing political situation with your allies and enemies, and it’s just easy to keep moving in that space.
But should you stop — your skill queue empties out and you forget what you were training to do, nobody in game remembers you anymore, your research seems pointless and you are no longer connected to the game. News of a griefer olympics makes space seem even colder.
It’s inertia, and it would take a powerful shove to keep things moving again.I've tried to describe this in terms of mmorpgs, that it's not so much playing as developing an inertia through a series of "well, this gets you THIS...and that gets you THIS...and so on and so on until you get this big shiney that the Jone's don't have!"
I think you can see the start of that documented in this penny arcade comic.
It ceases to be playing so much as a habit, much like maybe you use the same supermarket all the time to buy your groceries - it becomes a repeating habit. And as much as Tippa points out, when you pluck the inertia out of it - there turned out to be no desire to do the activity, barring the habit of doing so. Like if that supermarket closes for renovations and you go to some other place, maybe you just keep going to that other place even when it opens again.