Wasn't the most important factor Symbian being Nokias cashcow? That is what gave management justification to neglect other inhouse developments until all trains to successfully shift away from symbian had left the station in 2008.

In my interpretation, Nokia failed from its past success and not being able to turn its ships crusted steering wheel when they finally realized the size of the iceberg.

Timing was key imo. There had been a short window in 2006-2007 to realize the impact that Apple would make by turning the game from business and nerd tech into some awkward NLP inspired mind control like emotion based thingy. Nokia Board had a leaked iPhone on the table according to another book i read but did not draw the right conclusions or just could not comprehend completely at the time. Which is admittedly really hard to judge from the pure device without knowing the strategy behind it i guess.
Don't know if Google board was genius or lucky but they where able to hit the market with a competitive product, slamming into the low price segment Apple "left for them" with full financial force.
Elop was just a symptom of Nokia Board grabbing for the last weathered straw imo.