They don't have access to antiparasitic medications, for example. Another example, they don't stare at screens ever. Plenty of our habits are better for us and plenty are worse, and the same is true for them. I'm sure plenty of habits of all people have trade offs. We have a higher life expectancy. What's a better metric for healthy lifestyle than that? It doesn't mean everything is better, but it is a good yardstick for determining if we are doing more right than wrong to our health, all in all.
So just "this is how it's done in nature so we are wrong about how we do it" isn't a good heuristic. A dog will lay on something soft given the opportunity.