One of the "Generations" writers joked that they figured people would change uniforms only when they showered - this is supported in dialogue when the Kleavage sisters noted that Geordi had bathed after he got back and before he went to engineering to provide them with their plot device. This makes it wierd when you notice that by that logic Worf did not shower over the course of the movie, but the women didn't either.
It did readily show that they hadn't had new uniforms made for the film, except for Stewart. Frakes and Burton visibly had fit problems in their outfits (look at their sleeves) and of course the women didn't have tailored, form-fitting costumes either.
We also know from various sources that the TNG uniforms weren't very comfortable to wear. The early spandex ones caused pain in the lower backs where they compressed the spine, and the latter two-piece costumes (for the guys) still had pants that were not comfortable and the upper tunics would ride up, resulting in the infamous "Picard maneuver" of straightening it out whenever he got up. The later DS9 style had a cut that was more comfortable for both genders and were better tailored for different body types.
Still, while the cut of the DS9/VOY uniforms worked better, I never liked the black look with colored shoulders. Slimming as they were (especially for some of the guys in later seasons), IMO it never fit for a bunch of heroic space explorers to be walking around in ninja black with highlights. There were some early concepts for DS9 which featured the TNG design but with the DS9 front zipper and purple undershirt. I would've liked that as a compromise, personally.