Hi PJ2,
There was a post, #2062 by SaturnV on the R&N AF447 thread regarding the deviation ("Can you maybe go to the left?"). He posted a satellite weather overlay where this turn to the northwest occurred that was posted earlier by MM43. If this is at all somewhat accurate, it would appear they recognized the weather ahead (perhaps a little late) and were using their radar to shoot the gap between two CB's, the one on the right being slightly more significant than the one on the left. And as they did so, the turbulence increased and they reduced speed to MACH .80. They probably had no time to ask for a deviation at this point in time and it wouldn't appear they needed to deviate for very long.
Just some thoughts.