Taking a step back, someone said on this forum that Win10 shows a belief that desktop is dead but that's not just a Microsoft phenomena.
Google is only developing Chromium OS as a web connected client. Nobody would call Chromium a desktop OS in it's own right, nor does Google need to compete with Microsoft on desktop OSes anyways. Google is simply devastating Microsoft in the mobility space with Android. Despite folks thinking of smartphones when someone says "Android", Google made sure their OS runs on a plethora of tablets. Because Google pushed Android hard, it's almost saturated the mobile consumer market.
Apple does still develop OSX but that OS is focusing more and more on mobility. Obviously OSX isn't targeted at desktops given the ubiquity of Apple's laptop lines, and laptops are a consumer space where Apple is slowly eating away at Microsoft's dominance (and where Google's Chromium fails to compete). Looking a little closer you'll notice iOS features being (back)ported into OSX, like the Control Center. I wouldn't be surprised if Tim Cook eventually announced that MacBooks will soon run some variant of iOS and bring an end to the the laptop focused OS. :O
Microsoft? They've got to compete against Apple and Google in the tablet and smartphone market, but Microsoft's failed to do that when you look at the Windows CE history (which boggled my mind because so many corporate emails run Exchange; so smartphone integration was low hanging fruit). Basically Win10 is sending a loud signal that Microsoft is targetting tablets. Yet they don't want to unhitch from Microsoft traditional dominance in the desktop and laptop space. Instead of developing a separate OS for tablets (like Apple's iOS on iPad), Microsoft opted for a hybrid OS. Win10 is the crossroads -- and it's also a pain in the butt if you just want a good ole' desktop.