I think "application" is the wrong focus. The real thing to help students understand is this exact question: what is math? That remains a mystery to most students. It gets conflated with the problem of application, but I think the real problem is most educations don't make clear the idea of abstraction, symbol systems, and logic. When you don't understand something, especially why it might be useful or at least intrinsically interesting, it's hard to get motivated about it.