I like the fact that they kept the uniforms they did.
I'm sure the real (off-screen) reason was due to budgeting constraints. But I thought it made sense from a story perspective.
Once again, we are supposed to be on our own in the DQ here, folks, and replicating a bunch of uniforms when a) the old ones were in good repair and b) we are supposed to be conserving our meager resources, would have been not in keeping with the show's premise.
I love the FC uniforms and am glad DS9 moved to them. But the original DS9/VOY uniforms are my second favorite...and I'm glad they got a chance to continue their life on VOY. I think they look good - a classic design that will never go 'out of style'. Which is a plus, IMO, because I personally think the early TNG uniforms are doing NOTHING to prevent the aging of that show.