why… why does everything need to look the same, sell the same junk.

Because it is cheap. Build a warehouse, fill it with cheap shelves full of mass produced products. Costs come down due to economies of scale. It’s cheaper to make a kid’s toy if they are all made of plastic from the same mold, and it is cheaper to make buildings if they are all built from the same engineering documents. Stamp your logo on the building so that people know what quality of goods to expect at your store. You can now undercut local stores with lower costs. People shop there because they want to save a couple bucks.