Spectrum is kind of a weird case though because it kind of has to be monopolistic - if you allow multiple, independent systems to share the same frequency band, none of them will work.

> Suppose instead they held a new auction every year or every month for use of the spectrum in a given region until the next auction.

This would work if the government or some common third party were responsible for putting up towers (and lease them to the telecoms like MVNOs), but as it is the telecoms build and operate the towers themselves, and the hardware loadout changes slightly depending on which frequency bands that telecom is allowed to use.