Virgin genetic degradation isn't getting a chance to wipe-out banana cultivars.

Chad Fusarium fungus that gradually get better at proliferating in genetically-identical plants do the ''extincting'' job much quicker.

Fusarium fungus lives everywhere and is mostly harmless to healthy plants.

It has too many hosts, and can survive in soil too long, to be reasonably eliminated to grow again the previous cultivar on that same soil where fusarium got expert at killing it.

The Gros Michel cultivar, the one grown everywhere decades ago, was almost entirely wiped-out by such a strain of fusarium.

The killer fusarium strain got propagated around the world by contaminated equipment, soil accidentally transported, and already-infected young plants that weren't showing visible symptoms sold to other farms.

Since then, new fusarium strains evolved into all major banana cultivars, but better agricultural practice make their spread much slower.

There are several wild banana species. We don't commonly eat them ( some people do, usually by cooking them because they are hard ).

Wild bananas are smaller, harder, don't taiste very good, and are full of seeds.

But they can be used to make new crossings for seedless banana cultivars that won't be vulnerable to current ''cultivar-killer fusarium'' strains... untill another such strain(s) develops in some clonal population(s) and spreads the same way the other did.

Some labs are also working on genetically-engeering existing cultivars to change them enough for the narrow-focussed fusarium strain to be harmless to the modified version... but doing so usually changes the delicate balance which made that cultivar taiste good.

And new fusarium strains will evolve in this new hypothetical clone too shall it be mass-grown.

TL:DR : Other diseases eliminate banana cultivars long before genetic mutations do.