People who keep saying "it isn't hard" are confusing something. Even if it "isn't hard," it's still time consuming. It took them over a year to come up with a mac port. In the time it takes them to come up with a new Linux port, a new build or configuration could come out and they'd have to take MORE time to test for THAT.
And time is literally money since you have to pay your development team. And time spent coming up with a version that works on the Star Trek space anomaly that is Linux could be spend making sure the windows, mac, and PS3/4 versions actually work.
That's not to say I wouldn't WANT it to work...well, in reality I'm completely apathetic since I don't use linux, but let's be real here.