I thought it was because the chemical banana taste is just a bit different becsue of how it's made, but apparently it's because it's based on older bananas, as I found out in this article.

Big mike! Or gros Michel. Whichever you prefer to call it.

I have had Gros Michel bananas. They do not taste like banana candy, although weirdly they do smell like the candy much more strongly than the Cavendish.