Because if we were stronger, we would have extincted most/all other species and probably ourselves by now.
Because we spent too much time making spears and stone tools like a bunch of nerds instead of jumping from branch to branch and killing our prey with our bare hands like proper Chads.
Maybe a bit of context, I kinda injured my ankle in soccer. Our human bodies, are just to frail. Pittyfull!
https://www.dezeen.com/2017/08/27/graham-person-designed-to-survive-car-accidents-designs-of-the-year-nominee/