I see that being more of an issue of consistency than lack of effort, personally.
Given the fact that they seem to be putting a lot of emphasis on consistency, i believe that to be the case.
Look at differences in Halloween Town, Olympus Coliseum and Agrabah between KH and KH2. That isn't "consistency," (save OC) but it has the areas that count. And even IF they didn't do that, they could at least ditch some random less important areas and add others in different places. The only consistency they need is in the primary, significant locations.