I've a question about builds.

Obviously, a lot of builds on YouTube or whatever have wood or other rigid siding inside to make it look nice.

But I was thinking--why not, like, put rugs against the wall? Or fabric? Over your insulation? Why not some sort of cheap board that has wallpaper with a nice design pasted to it? Seems like a bunch of drapey fabric would both be lighter weight, and just as pretty. And some hard backing with wallpaper would be lighter and pretty too.

Is there a downside that I'm too much a newbie to get? Fire hazard? Moisture-trapping? Would it get dingy with dust or something?

(I could see wallpaper un-sticking with time, I suppose, moisture messing with the glue and making it all moldy, and perhaps that's why nobody I've looked at has done that idea.)

Or is it simply a cultural thing where everyone does wood because they saw it elsewhere and it looked nice, so everyone copies and doesn't think of alternatives?

I'm just trying to brainstorm here and figure out if there's a hazard I'm unaware of or not.