I’ll also mention Raspuri which is my favourite kind. As the name suggests it’s very juicy
The small yellow Indian mangoes that are exported also taste very different from the exported big green-red Brazilian mangoes.
So the export might have to do with it, but I think it's the type of mango that makes the difference.
I find Indian mangoes much better personally, even if exported, although when traveling in India they were even better.
Here in the US, due to industrialization, I struggle to find good fruit and vegetables in general, let alone tropical. They’re all picked too soon, travel too far, and have barely any flavor compared to home grown - and I’m in California! There’s a few specialized tropical fruit growers in Florida but it’s not even legal to ship much of that stuff here
Our house didn't have a tree, but you could take a bag and just walk around the neighborhood, because people put fresh mangoes on their fences for others to take for free before they spoiled. Naturally ripened mangoes are indeed on a different level, but they last so little before fermenting because they're very sweet.
NOTE: I work with natural and organic farmers in India to try and find a market for their produce.
Believe me when I say this - naturally ripened mangoes are on a different level altogether when it comes to taste. What you get overseas is usually not naturally ripened as the amount of wastage is usually quite high with naturally ripened mangoes.