There's enough blame to go around, and ultimately the most to blame was the board. However, Microsoft did play a big role in trying to convince Nokia to get their former VP as their CEO, which was their long con into getting Nokia to adopt Windows Phone, because Microsoft thought a company such as Nokia could surely turn WP's fortunes around.

But yes, Nokia itself was most to blame for its failure to "pee in its pants" and adopt Android when it still had 2x Samsung's market share in phones.