Why? The "wish to serve" leads many to apply to more than one academy. There's no data on that but I would venture a lot that most apply to more than one. They need no other reason than why "that" particular academy and which service they want to apply that education towards. So many choices, so many options...
Maybe "that kid" doesn't know, or care, when he's first applying what he wants to pursue...most don't and they explore the opportunities at multiple institutions. As the process evolves and the real home work begins, most come to an understanding of the long view...it ain't the school, it's the service.