Even a hero has to find a way to make some money.
I used to wonder why the people kept charging Link, or any other hero, for the items he needed to save their world. Then I thought, that maybe he wasn’t the only other “hero” out there and that just maybe there was others.
We never actually saw the others, but maybe there were more. This could be one reason they aren’t just giving him the items he needs to complete his quest. Another theory, is that the inhabitants of the world simply do not recognize Link as the hero or don’t think the world needs saving in the first place.
Nonetheless, it’s a lot of thought put into characters that repeat the same phrase over and over again regardless of how many times you talk to them.