Why is this a bad thing designers must be "guilty of"? Most websites are built around providing some sort of commercial service / product, so the number 1 goal

Why is this a bad thing designers must be "guilty of"? Most websites are built around providing some sort of commercial service / product, so the number 1 goal of design is to get out of the way of the user paying money and receiving service. If the design was radically different website to website for no other reason than artistic-special-snowflakia, then as a designer you're putting on extra cognitive load onto your users and forcing them to think about things that ultimately don't matter to either you or them. Literally everything from cars (colorful sells with engine in front and some seats in the middle, brake is left of the accelerator) to desktops (mother board, 4 RAM slots, 1 CPU slot, USB slots, etc.) to stores (carts out front, role of checkout stands next, isle separated by content after) benefits tremendously from standardization, and are what makes modern life even remotely livable.