Soft foods cause crooked teeth. Ancestral humans ate raw tubers and other very chewy things that exercised their jaws, and the growing human body needs this resistance/exercise. If you look at modern hunter-gatherer tribes with traditional diets, they have a far lower rate of crooked teeth we'd solve with braces than the developed world.

Sterile environments/too-low pathogenic load causes allergies. The immune system expects a base-rate of infection; if it doesn't see that, it upregulates. Allergies are a first-world disease; they're far less prevalent in less developed countries, and you even see the effect in immigrants- their allergy rates go up after a few years of living in a developed country.