HBO knows it's 2013. It's built a Netflix competitor. They have the whole tech stack for subscription internet streaming running and proven. They're signing 10-year content deals with exclusivity agreements that simultaneously give them a future catalog to rival Netflix while locking Netflix out of acquiring the same top-quality content. HBO has all its ducks in a row, it's playing the long game.

All they're waiting for is the tipping point in consumption habits. Today, most of their subscribers are paying $17+/month via bundling with cable TV, and every major cable provider in the country is heavily advertising them for free. The moment they can go independent and accept subscribers without going through a cable company is the moment the trickle of people dropping cable TV in favor of internet media turns into a tide. It's not today. If they split from cable today, they'd lose free advertising to hundreds of millions of people a year, and they'd likely earn far less per month from each subscriber they pick up.