The problem in the OPK years was that the Symbian team consistently was succeeding in frustrating the obvious line of R&D around Maemo and Meego. Nokia delivered a series of forever promising but crippled developer oriented devices. Not enough memory, slow CPUs, clumsy form factors, business decisions to exclude a phone stack from the N810, etc. On several occasions things looked like they were coming together, but projects were cancelled or converted to run Symbian instead of Meego. That was a combination of politics around Symbian and a near total technical leadership vacuum. OPK was a CEO with a financial background and he probably actually believed Symbian was good enough and a future proof strategy when it was quite obvious neither was the case. There was no real CTO in charge of the technical roadmap. Nokia fired and promoted away several executives to this position but it never amounted to a role that actually had impact. Even today the CTO is actually merely the head of nokia research and I doubt he takes decisions that either Nokia Maps or Nokia Networks care about.
Elop continued the tradition of not really giving Linux any chance whatsoever. He killed Meego based on the notion that it would take years for it to take over marketshare from Symbian. As we know now, windows phone had exactly the same problem. Meltemi was in an advanced stage of development when it was killed based on the notion that Ascha was good enough and that windows phone would scale down anyway. That too turned out to be a fallacy.
Finally Android was always a possibility. People think of Android as an OS. Instead it is just a runtime. It would have run fine on Meego, Meltemi and probably with some effort also on Symbian. Just like it runs fine on windows desktops, OSX, blackberry, and other platforms. Application compatibility is a business choice, not a technical choice. Probably if Nokia had take the obvious decision to support Dalvik on Maemo in 2008 (which ran Android just fine on my N800), it would have had a compatibility story around Maemo/Meego applications and a much smoother transition away from Symbian. The need for that was obvious around 2006 already for anybody in the business with half a brain.
Fundamentally Nokia was plagued by bad business decisions inspired by a fundamental lack of understanding of the technology, user needs, and market. Nokia killed their touchscreen version of Symbian at the exact same time Google bought Android and Apple got serious about the iphone (2004/2005 timeframe).