Although Luck wasn't exactly considered a ratings bonanza, Matt Zoller Seitz at Vulture.com argues that HBO's success is not driven by ratings, but rather subscription renewals.
What made this case unique ... was the nature of the show itself. No drama in TV history has been built exclusively around horse racing and the daily life of a track. Hollywood has used horses during production for over a century. Horses have been getting hurt or killed in production for just as long, sometimes because of negligence or cruelty but more often because of simple probability. When a story is dependent upon horses, over time it becomes increasingly likely that one of them is going to be hurt.
However, this 20 Minute Critic is more aptly to agree with one of the comments posted following his article,
This was a weak show that had the unfortunate side effect of being harmful to its equine co-stars. It never engendered much passion, except from critics, and it won't be missed. [Heliotrope]
Meanwhile, HBO will continue showing completed episodes of Luck. And in an effort to provide closure to the series, a script is in the works that will see Dustin Hoffman's Chester "Ace" Bernstein nod off after a long day of conniving and wake up the following morning as a Red Panda only to find a fat Panda taking a shower, realizing that Luck was nothing but a dream.