I don't quite understand... why is it that our society puts brains and brawn against one another as if they are opposite?

Generally speaking, people seem to think that tu can't be intelligent and physically strong in equal parts. Like someone who is very strong physically can't do very many tasks that are mentally challenging, and someone who is very strong mentally can't do something that is physically challenging. Why do so many people think that you're either one o the other, and why do people strive to be one rather than the other? Can't we all strive to be equally as capable in one side as we are the other?
I'm not saying that all people are like that, I know a handful of people that don't think that way, but it seems like many people do. Is there any particular reason that anyone knows of?