I think some of that is aesthetic, compared to the burro banana, the Cavendish is certainly more elegant looking. Burros are the ones you tend to see in most Latin American markets in the US, plump and stubby. They are no less tasty however.
Some of the other such as plantains aren't very edible raw which is why you seem them flambéd in deserts and fried into chips.
I have fond memories of very short and sweet bananas in the French Caribbean and Vietnam, I wonder if it's the same variety. I would also describe them as more moist.
Vietnam was most likely "Chuoi Cau", they look like burro bananas but are very sweet and easy to peel?
Interesting that you bring up Vietnam because it looking increasingly like they are looking to be the largest banana supplier to Asia, soon to overtake the Philippines. There was a big splash in Japan last year when Vietnamese bananas showed up in Don Quijote a discount chain in Japan.
I recall eating the best bananas I've ever had when I was in the Dominican Republic. They were a little short and thicker, but much denser and more moist (made the US Cavendish seem dry and lightweight in comparison) with a great flavor. I don't know what variety they would have been.
I'm curious as to why more varieties are not available globally. I guess I'll have to wait for the next part.