Because sometimes its better to not ask if you can or should and instead try. It was obviously popular enough that it still has a soft spot in many tech enthusiasts’ minds. And arguably its the element of any OS that you encounter the most. Going from your home computer to even just a computer at the public library, one thing was almost guaranteed to be the same and that’s the desktop background.So why not make it really high quality? They had no idea how far resolution would come and what would end up being sufficient, but because of their decision, even now people seek out that image for their desktops.