I believe a complex visual environment is a part of this. Bare walls…bad. Art prints, bookcases, windows, toys, light-and-shadow…good. This is part of why we hang mobiles over the cribs of the very, very young. Our brains are built around interpreting our visual environment, and complexity is healthy.
I would guess that the same is true for the audio environment. Have some nice music going in the background. Lots of people leave their TV on all the time.
Environment is definitely a part of it. But even in that category, I’ve seen big differences in how people keep their homes. Some people like to have every square inch of wall space decorated. Others prefer a more Zen style–blank walls and little to no clutter.
My wife likes to watch HGTV. While there are a few programs that focus on “unusual” homes (yurts, castles, tiny houses, etc.), the vast majority of interiors that they show are basically different configurations of drywall boxes. Although this is probably a practical consideration (box-shaped structures are easier and cheaper to construct than round ones), it’s not often that someone insists that they must live in a round house (at least, not in the US).
Of course, the homes have very different exteriors, and are set in very different locations (rural, urban, seaside, etc.). So the views through the windows and amounts/quality of light are also different. But humans do tend to live in boxes (and to a much lesser degree, tents, yurts, castles, etc.). That’s one quality that seems to apply globally, in terms of environmental enrichment.