It is legacy broadcast regulations stretching back to before the days of rock and roll (possibly even before the Great Depression).
Really outmoded concept these days.
And unfair when other nations aren’t expected to uphold the broadcasting standards.
Overlapping AM broadcast frequencies and weak night signals (and that terrible time around dusk (when station signal strengths change non-concurrently)) are annoyances of the past.
It's the new world order as demonstrated by Disney's changes.