Because most people suck at taking abstract mathematical concepts and seeing how they could apply to code. Including me. Let's take the definition of a function:

> A function is a relation for which each value from the set the first components of the ordered pairs is associated with exactly one value from the set of second components of the ordered pair.

Cool, I have no idea what the fuck this means and how it is useful to me.

Oh wait, I use them every day.