Apparently you never heard of the Burning Platforms memo.
We'll never know if Elop was actually a mole inside Nokia,
But just when maemo/meego was stable enough to depreciate Symbian after >10 years of development, they choose to throw everything away and go the W7->W8 way.
This decision was made when Nokia still dominated the smartphones market (yes, Symbians were smart phones), android was a bag full of crap, and the Iphone 1 was prettier but inferior than the N900.
I think W8 lumias were grate phones for people who don't care about apps, but arrived too late.
Meanwhile in a parallel world, Nokia's meego might have stood a chance (or might lay somewhere between Palm and BlackBerry )