Not American myself, but I can think of a few factors besides meat:
less stress
less polution
less processed food, be it meat or not
less sugar
less sedentary lifestyle
genes
Nutrition alone won’t get you to 100. Having a diverse diet keeps ypu healty, but there are many factors that impact health. I do agree that meat is overused in general population, but can’t really force the vegan/vegetarian lifestyle onto an omnivore specie.