Spectrum should’ve been a shared resource from the start. It’s scarce because there’s Massive amounts that have been purchased just to stifle competition and isn’t even in use.
Funny, for all those reasons 5g has moved to a shared model.
As an electrical engineer, I am honestly astounded by how well spectrum has been allocated/shared. It's one of the greatest miracles of the modern era that tens of thousands of antennas can simultaneously jam into a stadium and still have cell service, radio, TV, wifi, walkie talkies, and
Bandwidth is scarce because it's limited by physics. There's some minor inefficiencies, but it's generally pretty good, in terms of bits per second per Hertz.
Spectrum is actually limited and cell towers aren't free.