I imagine part of it has to do with the material itself. When it comes to wallpapers and such, more textured surfaces are easier to work with because they have a larger surface area for adhesive, and wallpaper is something you want staying stuck to your walls for some time! I think the same goes for paints, to some extent.
Aesthetically, textured surfaces are more interesting than flat, completely smooth surfaces. All materials in this world are textured to some degree, and it’s only man-made materials like metal and glass that appear completely non-textured. Being in an environment with completely smooth walls would seem sterile and artificial, generally not the kind of environment one would want to spend a lot of time in, IMHO.