Microsoft has a different set of problems. Windows Phone is already shipping, so adopting Android would actually delay the next release. What they need is a stronger ecosystem—more apps to bring users and more users to bring developers. Adopting Android might help them achieve that, but at the cost of ceding control to Google. At the end of the day, why would anyone buy Android from Microsoft instead of Google?
If they can't make a success of Windows Phone, MS would be better off to just can it and provide apps and services to both iOS and Android.