Nokia felt that they had a better opportunity to capitalise on their strengths by going Windows Phone over Android or Symbian/MeeGo. I had the Nokia N97. Although I consider it the worse smartphone ever, it still had a few things that impressed me at the time that I would have liked to see from other manufacturers.
One thing that was very good on the N97 was Ovi Maps, Nokia's mapping app. You can use it offline navigation and it has lane guidance. These are the two features I would love to see on Google Maps.
Nokia lost me with the N97 and the subsequent E7 was not good enough compared to the HTC Desire Z which I ended up getting at the time. Still, if Nokia made an Android phone, I will definitely consider it. The main thing holding the N97 back was the crappy software. The only reason I kept it for 7 month was Ovi Maps and Opera Mini. Finally I had enough and left. The N97 still has the best landscape slider keyboard I have used by far.
I have not been impressed with Windows Phone. It has nothing that would make me want to make a jump from Android.