One of the things they have that people in developed economies generally don't is a 50% infant mortality rate.

The ones that don't achieve it through access to very unnatural artifacts such as vaccines that are quite likely to have been made using ultramodern technologies such as genetic modification.

Or, I've got quite a few friends who have various congenital conditions that mean that they absolutely would not have survived in a society with a more "natural" foodway. With the modern food supply chain, though, they're doing just fine. Unnatural things you get in some ultraprocessed foods, such as vitamin fortification, mean they can even do it without having to worry about developing comorbid chronic ailments due to malnutrition.