The hierarchy of "The Department" were also almost all ex pilots or ATC. If it needed controlling, ATC did it, with or without radar. Money was pretty much no object back then, so CTA was just extended to provide whatever was needed. Remember the vast majority of airspace was uncontrolled, so turning little bits of it into controlled was no big deal and accomplished by the stroke of a pen.. If a jet went there, it got CTA and a tower. Why didn't FS use radar? Ask DCA or Civil Air.