I think a lot of it is because they have quite a small team working on it, Square have quite a lot going on at the minute with Lightning Returns, FF XV and they've recently finished games like Hitman and Tomb Raider in the time FFX HD has been in development - and don't forget X-2 has been done as well, and having played a few of the HD updated games this one looks to be by far the best so I for one am glad they've taken their time to do it properly.

Also they had to get the original voice actors back to record the English language version of the international edition, which is partly why the Western release is three months behind that of Japan.