Comment by achierius

Desktop operating systems != phone operating systems. You need to have a lot of support for things like "sleep apps you're not using right now" or you'll burn through battery. Not to mention that we tend to expect a lot of functionality which only works when the OS enables it, e.g. the sort of app-to-app coordination enabled by Android's App Intents. You certainly could build something like that on top of DBus, but, well, you'd have to build it.