The theory I described is not that the Sony/the media pressured the FBI to blame someone, but rather that the FBI saw a high-profile cyber attack and internally decided that it wanted to project power by pretending that it can solve this type of case.

Or perhaps an individual in the FBI running the investigation wanted to project confidence to his superiors, and made a public statement. At which point the FBI felt that it could not backtrack and decided to double down on its confidence.

Or maybe there was a filing error where a low level secretary checked "North Korea, definite" instead of "Uncertain" on the paperwork, and the FBI is again doubling down on its original public claim.