Comment by royal__

As others have noted, the problem is often with keeping servers running. It's impossible to predict how successful a game will be in the long term, so the publisher can't make any claims to it's longevity. And, it doesn't make any sense to keep servers running if there's not enough income flow. Where this is really an issue is MMOs. Games like Forza already have some solutions: online features are eventually disabled, but you can still play the core game.