Why hasn't Google given Microsoft the coup de grace and actively developed some desktop/laptop distro ala Chromebook but without the stupid "web only" focus?
Because that wouldn't help them. Google is all about ads. They developed Android only because they were afraid they would be locked out of the emerging mobile systems.
There is no sign that desktop operating systems try to get rid of the browser. The only way to sell more ads on the desktop is to make the browser the OS. Which is exactly what Chrome does.