That was a budgetary thing more than a plot choice.
I don't really but that, we saw some great sets in the course of Voyager. Sprucing up the ship and adding a new set or two would not have broken the bank.
I mean space station sets and Planetside sets more than sets within Voyager itself.
Some of those sets you're talking about may have already been re-used ones to begin with (they re-used stuff from FC and INS). All the Borg sets were from FC, and the big holo-museum from "Living Witness" was a re-use of an INS set.