Do they have the "snob" or "materialistic" trait? My materialistic sims do this a lot, especially the one that has materialistic and snob. It's annoying. She kept doing it until her roommates started painting masterpieces, and got rich enough to make the house real fancy. But then she got pregnant and moved in with her boyfriend, and started doing it again. Her boyfriend is making more money now, so her house is getting fancier, but she still complains (not as much as before though).
OTOH, my outgoing, clumsy, erratic guy is perfectly happy living in a tiny studio home with no wallpaper, flooring, or decorations.