Because every engineer who comes up with a new innovation practices far more than math and engineering. They also use communication, creativity  and artistic skills to bring those innovations to fruition. The arts are a great learning tool and can serve as an on-ramp to STEM for underrepresented students or enhance existing education.  Having Air Force professional musicians visit schools allows the Air Force to use the "A" in STEAM as access to provide an introduction and storytelling element to highlight other Air Force mission areas. Engaging students' strengths using art activities increases motivation, access to schools, and the probability of STEM success.