It's a nice looking display, and it's running at a nice 60FPS. However, operating systems don't generally run in full GPU mode all the time -- it's a huge amount of power to be re-drawing the screen that often, and that scales to poor battery life on mobile and expensive power costs in servers.
So that's one of many reasons practical OSes don't do their UIs with GPU shaders when they can otherwise get away with less.
So that's one of many reasons practical OSes don't do their UIs with GPU shaders when they can otherwise get away with less.