Ever read USAF Col. John Boyd's biography? He developed of maneuver warfare and pretty much invented warfighter doctrine adopted by all the modern air forces around the world. He generalized his ideas, and it became a core part of US Marines doctrine. However, the generals in charge of the USAF rejected his ideas. In their minds, you have

Boyd was the one who pushed to developed the F-16 based around the ideas maneuver warfare. (The F-16 was designed to out-maneuver anything else). One of his disciple was the one that developed the A-10, specifically for close-air support mission, using the same principles applied in a different way.

CAS missions was something the USAF inherited back when the organization was part of the US Army. It's treated as the step-child that the USAF "bomber generals" don't want, and want to get rid of, and can't because that was part of the original agreement when the USAF was formed as a separate military organization. In their minds, if you develop a plane that can fly fast enough, stealthy enough, and click a button to shoot out missiles, then you don't need to be agile at all.

The politics around the A-10 is discussed thoroughly in Robert Coram's biography, "Boyd: The Fighter Pilot Who Changed The Art of War". Boyd has been dead for about 15 years now; what I'm reading here, the same politicking is still going on.