Maybe because these banana breeds don't take lightly to the multi-week shipments required for bananas to be eaten in Europe?
Brazil's a big country too and it's not like all the bananas are grown an hour outside the cities or anything. These sit around in supermarkets, they're not delicacies you have to find at a farmer's market that go bad in a day or something.
I really wonder if the issue really is just lack of awareness. I can't count the number of articles I've read that basically lead you to think Cavendish is the only banana being grown at large scale anymore, when that's just not true.
And here in NYC a lot of the produce I buy comes from Mexico at scale, including things like ripe cherry tomatoes grown in greenhouses that are much more "luxury" than bananas. But also just everyday papayas and avocados.
So given that so many fruits and vegetables are already cultivated at scale for export from Mexico, it's not clear why banana varieties are that different. To the contrary, all sorts of new fruit varieties are being invested in, grown and shipped from other countries. Just yesterday I bought cara cara navel oranges and blood oranges too from my normal average supermarket, which certainly weren't available here five years ago at an average store.
Being simultaneously soft enough to eat raw and durable enough to ship and store is really threading the needle. There are many varieties of plantain (it's hard) and many varieties of bananas that are hard to ship. The Cavendish is often the only fruit available at convenience stores, maybe alongside a few oranges, because it's just so darn convenient.
I would think it would have a lot less from being some actual boon from the gods and more a fruit in limited supply in the region of interest.