You forget about the splitting of developers were a new project to emerge.

Microsoft failed, partly because it was as of yet not a big enough platform to target by other developers - they have enought things to do with android and apple. A new platform can’t emerge unless there is some incentive for developers to target it. Linux phones are in a special circumstance, because apps are developer for them out of a hobby. But phones are a main social device, you can’t have one that doesn’t have your bank’s app on it for example. Linux phones must emulate android (and it is sort of working, fortunately) to remain afloat.