As you may be aware, upstream GNOME team decided to remove the handling of desktop icons from the Nautilus file manager, moving it to the GNOME Shell user interface through an extension. The change will take effect with the upcoming GNOME 3.28 desktop environment, due for release on March 14, 2018. While the GNOME devs didn’t offer any details on this major change until now, as they are probably still trying to implement the handling of desktop icons in GNOME Shell, it would appear that the Ubuntu Desktop team decided to play it safe for now and stick with an older Nautilus version, such as 3.26, because “it works.”