First, it's Trek.
Second, there's no supply reason that Voyager couldn't have changed uniforms at ANY point in time. In Trek, you have several different "god" devices which, when combined, pretty much eliminate anything resembling "limited resources":
An economical and efficient anti-matter reactor.
the transporter
the replicator (an outgrowth of the transporter.)
Put all three together, and there's no reason that the Voyager crew couldn't have had new and different uniforms every day. None. As long as the ship's reactor kept running.
It's Trek. It stopped making sense a long time ago.
Tarek