True those platforms have security controls, better than what we've ever seen on desktop. Desktop also needs controls like that: to use the system tray, filesystem, hardware, etc. There's at least a work multiplier of 3 for Windows, Mac, Linux. It's just one of many things needed.
Building the web toolkit took enormous effort and it sucks in many ways (see article). Theoretically a new one could be created and could also work for desktop, but there are lots of reasons why that won't happen.
Building the web toolkit took enormous effort and it sucks in many ways (see article). Theoretically a new one could be created and could also work for desktop, but there are lots of reasons why that won't happen.