Why do moths exist? If they are just food for something else, why can't that something eat something else?

I am equally grossed out by moths and butterflies, but I feel like butterflies are at least considered beautiful to most people, so I am narrowing this down to moths only. (The caterpillars we get have red eyes and turn into moths. They fall all over my car, and they make nasty cocoons on the ceiling of our back porch. What’s even worse, is that when they hatch, they don’t take their nasty cocoons down, they leave them there for me to get rid of! JERKS!)