From FAQ on the Stop Killing Games page.

Q: How are publishers ‘destroying’ videogames?

A: An increasing number of videogames are designed to rely on a server the publisher controls in order for the game to function. This acts as a lifeline to the game. When the publisher decides to turn this off, it is essentially cutting off life support to the game, making it completely inoperable to all customers. Companies that do this often intentionally prevent people from ‘repairing’ the game also by withholding vital components. When this happens, the game is ‘destroyed’, as no one can ever operate it again.