But that is the region where most developers would want to target to get more revenue
Combine with that other markets also getting bigger like South America.
The reality is that NA had their smartphone / mobile boom already and the rest of the world is still catching up. There are more smartphones, apps, features, services, etc. to be gained by selling to the massive influx of new customers versus trying to cater to the old audience of North America.
In the vast majority of cases, Asia and SA won't touch your product if you don't have deep familiarity with their markets, their idiosyncrasies and have a competitive business model there. Getting folks in these markets to pay isn't easy, friend.
And that's why we keep having these conversations in English on a US site about products made by US companies.
I agree that if you just check a few boxes and make your app available in those markets you won't see much success.