The Federal Communications Commission (FCC) was established in 1934 when radio was less understood than it is now. Back then, we had only primitive receivers that couldn't handle more than one transmission on the same frequency. Multiple transmissions at the same time was called "interference", because with your primitive transmitter, the other transmission interfered with your ability to hear the first.
The FCC assumed this was just how radio was. If only one person could speak on a frequency at a time, then it was their job to make sure that only one person did. They divied up the radio spectrum and shut down any "pirate" stations that tried to use a frequency they had assigned to someone else. This was just How Things Had to Be, they said.
The FCC has done just that. The map of allocated spectrum looks a little like some strangely-colored drawing of Zeno's paradox, where at each step the hare only gets half the way to the finish, so he never quite makes it there. Spectrum allocation seems somewhat similar, each time we allocate about half the spectrum, because that's what current technology requires. But then we come up with innovative new ways to pack more stuff into smaller space, so again we only need half of what remains.
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