That's because the most popular theory of tinnitus says that it settles into the brain after a few months. Otonomy is playing it safe. For their Phase I trial they only allowed patients in if they'd had tinnitus for less than 6 months. In Phase I they saw no decrease in effectiveness for patients near the 6 month mark, which is why they opened up the trial to patients who've had tinnitus for up to 1 year for Phase II. If they continue to see no decrease in effectiveness I imagine they'll probably keep expanding the window.
Though then again, I was reading up on minoxidil (Rogaine) and learned that they only ever did studies for the crown of the head. So all Minoxidil products have to legally say it only works for hair loss on the crown (because that's what was tested). However, there are tons of anecdotes online from people who say it works for their hair line and there are communities of people who say it works for beards (with some neat before and after pics). So if Otonomy doesn't expand the window for Phase III, we may be in a situation where there's a drug that possibly works for us but we can't use it because the studies were only done on patients who've had tinnitus for a short time. I hope this doesn't happen and that for Phase III they try the drug on patients who've had tinnitus for a while, but it is a situation we could wind up in.