How do you imagine this would work even in theory? Running two OSes side-by-side (one when in phone mode, one when in desktop mode?).
Or running two largely incompatible desktop shells with largely incompatible interfaces for multiple apps (touch-optimised programs are very different from mouse-and-keyboard-optimised programs)?
For applications there is lots of work to make it really nice. Putting mobile apps on "desktop" can be done, while user interface will be a bit strange. But that's a thing which needs time. Microsoft tried that by pushing mobile on desktop, but they didn't have the mobile story. Apple has notable Userbase on both.
Userbase has nothing to do with that.