Since HBO shifted their focus from simply airing just-out-of-theaters movies and boxing, into becoming "not TV" but something substantially more, they've never been the place to go if you're a TV producer looking for a long-term commitment. To get all baseball analogous on you, they're kind of the Oakland A's of television.
Sure, The Wire eventually got its five-season run, but every year wrapped up with the distinct feeling that it could be the last time we'd McNulty and Bunk. I don't even want to talk about Carnivàle, which had its plug pulled with a third of its story yet to be told, leaving behind an exquisite corpse, sure, but one with plenty of promise never to be fulfilled. And let's not forget that Deadwood was originally supposed to be four seasons. (Or, at the very least, another pair of two-hour TV movies that HBO promised to produce after the rapid Deadwood fan base promised to gut the cocksuckers for prematurely cancelling their show — anyone else remember that promise?)
So this news that HBO has gone ahead and already picked up Luck, David Milch's new drama about the machinations in the underground world of horse racing, for a second season, after just a single episode has aired, is a bit out of place for them. Maybe it's a late payback to Milch for that final season of Swearengen & Co. sadly left to the imagination.