Could be because this promotes a bad UX? In GNOME, you have a dock for your most used applications, which can be launched or navigated to with Super+1/2/3.., there is the apps menu accessible with Super or by clicking the top bar, where you can organize apps as well as search for them. Desktop icons are distracting, and requires you to remove windows obstructing them to access the icons. If every DE just mimicked windows, we wouldn't ever be able to move forward. Though KDE is there for you if you prefer the windows way.