Wow, you sure are confidently incorrect. There’s paneling, wainscoting, and shiplap to name a few appliqués. Some people even build false walls to install pipes, cables, or extra insulation. It also helps with hanging things like TV’s or family photos. Not like a fucking tree house XD. Additionally, some old brick buildings you can’t modify due to historic building codes so the only way to “modify” the structure is to build around it.