The particular problem strain of the Panama disease affects the Cavendish specifically. This has happened before; the Cavendish, itself, only became the dominan

The particular problem strain of the Panama disease affects the Cavendish specifically. This has happened before; the Cavendish, itself, only became the dominant cultivar after other strains of the same disease killed the previous dominant cultivar, the Gros Michel. All members of a given cultivar are clones, so they're genetically identical and thus very susceptible to being wiped out by disease as they have no mechanism to evolve resistance. We'll probably just have to switch again.