newtonian mechanics - Why is small work done always taken as $dW=F cdot dx$ and not $dW=x cdot dF$?

I was reading the first law of thermodynamics when it struck me. We haven't been taught differentiation but still, we find it in our chemistry books. Why is small work done always taken as $dW=F \cdot dx$ and not $dW=x \cdot dF$?