This is my conclusion. There was a period when they were making a lot of noise about how they were making Flash "touch friendly", releasing Air across all the platforms, etc. As time went on Flash became tolerable (and useful!) but never really "good" and I suspect the real killer was that Adobe started to see dire feedback in their sales pipeline because people were prioritising iPad and Adobe could not offer a universal solution. Then I think, as others have said, Google decided Flash support was hurting Android instead of helping it (once you have critical mass, cross platform tools become a competitive disadvantage instead of the reverse) and probably told Adobe they were on their own and that was enough for them to decide to kill it, and killing it swiftly and making money from people forced to convert was better than killing it slowly.

I do think they really tried, for a while, but it just didn't work.