[xorcist]

WP8 was also a rewrite, for exactly the same reasons. It wasn't great, but if it was kept stable for long enough then maybe partners would eventually come back to build that ecosystem.

I guess the reason for this constant rewrite-itis is that Microsoft is still really, really strong on the corporate desktop side, and they desperately need some way to leverage that on mobile. Otherwise they are just too far behind to avoid being yet another OEM.

As you said, it probably looked good on paper. They do have deep pockets however, and probably afford both one and two more rewrites and still compete. They've done it before.