Becaus Voyager did have the resourses.
There were plenty of episodes revolving around them not having enough resources to so much as feed themselves, yet they waste resources on
paint?
To fill up the replicator all they have to do is stop by an astroid belt.
And mine the asteroids. And process the minerals they get. And
then put them through the replicator.
Also, the same would have held true for Ransom's ship, yet that was in pieces.
Fixing things up would give them something to do. After all Voyager is there home so they would want to keep it looking tidy.
There's a bit of a difference between "keep it looking tidy" and "wasting reources on paint and new carpets".
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