It was a festival movie and didn't receive wide release in September. Many places premiered it in October and November for example. Since it's a European production it no doubt had European distribution long ago. US distribution probably came around later and fitting it into a busy North American movie schedule was probably difficult. This is all just conjecture of course, but at least it makes sense in my mind.

Definitely looking forward to seeing it. I just saw Superman Returns and need some decent cinema on the horizon to help me forget it.