> The Linux kernel does seem to be good at that last part, but not the desktop projects.
That's because there are a shitload of them, there's way more than just the big players KDE and Gnome. Then the stack is highly complex with technology in the mix that is decades old (X11 dates back to 1987, that stuff is older than me!), and political infighting between competing (corporate or personal) interests doesn't help this either.
Android has multitouch solved, but at the cost of building everything from scratch and lots of stuff still being kept in proprietary firmware blobs for touch controllers. And there is only one Android stack, not two dozen...