The FCC justification has always been that the airwaves are a priceless public resource, thus subject to stringent government control with strict allocation policies. Historically, the FCC has been extremely punitive against any infringement, levying draconian fines and punishments against violaters of the airwave rules. Thus, "pirate" radio is regarded with the same contempt, fear and loathing as a turd on a State Dinner serving plate.
Community "free" radio gets an equally harsh regard; rules allowing limited range, low-power license-free community FM broadcasting are so stringent as to be a practical prohibition.
The FCC regards the US broadcast spectrum as its private fiefdom, doling out licenses and auctioning spectrum only to suitably qualified (wealthy) Corporate Oligarchy. It's an insanely paranoid and jealous, locked down bureaucracy ruled by autocratic overseers.
Imagine the FCC Commissioners' frustration that they have not yet succeeded in controlling the internet in similar fashion. View their actions through the lens of radio airwaves history and all becomes crystal clear.