I'm not a big fan of the series, but I can't help but think this smells fishy. To be honest this game is wildly popular over here in the US, and it's become pretty iconic all told. Localizing these games hasn't really been an issue for all the others that have made it over here and succeeded, so what makes this one differant?
In general, I'd immediatly suspect it's the "usual" Japanese barrier of racism. The attitude that something coming to the US cheapens it, or simply the fact that it appeals to the Japanese audience for them to have something the US wants but can't have. It's been a while, but when I used to read translated Japanese periodicals I remember some rather frank discussions about this kind of thing.
While it's been... wow, almost a decade, since I was into that kind of thing, but when it comes to Capcom I notice that a lot of things they produce don't wind up making it to the US market under similar claims that don't really hold up to examination. I mean when you look at things like "Namco X Capcom" and various crossover titles through the years, there are a variety of reasons given why they don't make it, but the bottom line seems to typically come down to there being no good reason at all....
In the end I tend to think back to "Final Fantasy X: Final Mission" and "Final Fantasy X: International Edition" (with expanded content) and why they never made it to the USA. The bottom line according to what I was reading at the time was that it was to throw a giant middle finger to the US. I suspect that's what's going on here since when I hear after all this time and the games that were released that suddenly it's not profitable to localize and import Ace Attorney games it's just ridiculous. It's like if someone at Nintendo was to say that Pokemon isn't popular enough to turn a profit. Differant scale of product/success, but just as ridiculous.