Hm, I'd have to guess, but I think all the competition from the Cannas growing around it might be what's holding it back.
Bananas are heavy feeders and like a lot of water. So do Cannas, so they are definitely robbing water and nutrients from the banana. It needs a big space all to itself next year. Roust out the Cannas and move them at least 4ft. away from the Nanner.
