Because, to be clear, what is being sold is a license, which is, in effect, simply permission to install and play the game. It is very much likened to a "subscription" because customers don't actually "own" any part of the game at all. They simply own "permission" to install and play the game. And there are all kinds of restrictions to the license which includes transferring the license, reselling it, etc. which are all covered in the license agreement at the time of purchase or prior to install, which of course, nobody reads. :)