Answer:  Are you kidding? Calculus is probably the most widely applicable mathematical subject in the history of the world. Every physicist, chemist, economist, engineer, in fact, anyone who is studying something which has quantities which are related to each other in some tangible way uses calculus. The reason we don't focus on applications is that since everyone in the class who ends up using calculus will probably use it in different contexts, it makes more sense to spend our time learning the basics of calculus and letting the various applications arise in the course of studying whatever you choose to specialize in later in life. Also, most interesting applications are also very complex, and we don't have the time (nor do I have the expertise) to study something like a detailed engineering application.