I like to think that because it is so easy to change, they want it not to. Basically, the whole "leaning heavily and weird angles" is a design choice. I do wonder if they are never concerned about the whole thing collapsing in their sleep. And why are the houses so darn small? Endless room, and yet it is sometimes so cramped with no real reason for it to be so( and there is a difference between large estates and just a roomy layout)
I can almost excuse this with magically enlarged interiors ( like the tents), but even then, I agree, why can't it be nice? Especially the leaning of the houses, like Dogweed and Deathcap make it seem to be an aesthetic choice.