Because it does its job so well.
Air Force zoomers hate the job of direct Air Support. It’s time to let each force provide air support for their own. A marine pilot will go all out in providing support for fellow marines, so will an army pilot for their soldiers. Presumably the navy already has plenty of zoomer aircraft.
Just to clarify, every A-10 driver I've spoken with just love that big ol' hawg and CAS. It's the fighter and bomber mafias which hates CAS and, by extension, the A-10.