Would that be so difficult? Think a Nokia 1020 with Android loaded on it. Or a Nokia N8 (Old gen) with Windows OS. Life would have been so much better.
Making life easier for you is not (and has never been) any device maker's goal (despite the ubiquitous propaganda); _making money_ is. I see no practical way for MS (or Google, or Apple, or anyone else) to make money __by providing an alternative to their cash cow__. That's not to mention that support cost would jump to more than double the size of supporting a single OS.<p>Edit: oh wait, I do see a realistic (i.e. evil) way of "providing an alternative":
1. make a deliberately crippled version of Alternative OS
2. provide alongside Our OS
3. wait for the negative backlash about the crippled version
4. gloat about the superiority of Our OS
5. Profit!!!