News for Free?

Why do news organizations give news away for free?

There would be a couple of components to this answer. First of all, game theory. I'm thinking of a prisoner's dilema where all news providers would be better off if no one offered news for free. But each individually sees a benefit to free news. The huge traffic to their website would increase their advertising revenue greatly. But if one newspaper provides free online news all organizations find it in their interests to follow.

Actually setting this up to require understanding the trade-offs between online advertising, print advertising, and subscription fees.