There's an enzyme in bananas called pectinstearase.
This enzyme helps the reaction with the naturally occurring ethylene in the banana (it's what ripens them). That reaction breaks and terminates some of the natural polymers that make up the fruit's fibers.
If a crop of bananas were to be lower in that enzyme, those reactions would slow and the fruit would still be loaded with the longer, unsubstituted chains.
Since those chains make up polymeric fibers, just like in rubber & plastics, the rigidity & elasticity become a function of those longer, undisrupted chains.
Like I said, I'm guessing because I don't know how much enzyme content is normal and what a reduction would have to be to interfere with that polymer size reduction.
But, the chemistry I provided is accurate.