The nice thing about those are I can physically close the laptop or turn off the phone. With a virtual screen, I have to use some UI to do it. I know it doesn't seem like much of a difference, but to me, there's enough lag and lack of real feel of control that I'd prefer a real object than a virtual one.
Interacting with app windows in 3D space also doesn't feel any faster than just using a flat window on a flat screen. I'm already super productive using keyboard + mouse and a flat display, so I don't see how using my voice and turning my head to look at things in a virtual space is any better.