Wireless mics were originally intended to be used as part of broadcasting. Essentially broadcasters had a license for some assigned bandwidth and part of that bandwidth could also be used for auxiliary services including wireless mics. Thus
VHF and
UHF wireless mics are considered part of Broadcast Auxiliary Service and fall under the relevant legislation.
Since analog broadcasting required buffer channels between local broadcasters and many channels were often not in use, it became common practice to use unlicensed
VHF and
UHF wireless microphones in the unused spectrum, keeping in mind that since completely legal use of the equipment was, and still is, possible by licensed operators it was the operation and not the equipment that is at issue here in regards to licensing. However, the
VHF and
UHF spectrum have always technically and legally been reserved for licensed broadcasters and thus most wireless mics operate in spectrum that was always legally limited to licensed broadcasters.
I say most because there are indeed wireless mic systems that operate in 'license free' spectrum such as the Sabine 915MHz and 2.4GHz systems. Operating in such spectra, which are also used for other purposes and by other unlicensed users, has its own problems. The possibility of a dedicated spectrum for wireless mics, such as exists for FRS, GMRS, CB,
etc., has been discussed, however it would have to be outside the
current VHF and
UHF spectrum as those frequencies are already assigned for other uses. That would mean that while there could potentially be a 'legal' spectrum reserved for wireless mics, it would be limited and not compatible with existing systems. Making this even more difficult, the frequencies likely to be available for such a change at this
point in time would tend to have their own disadvantages for wireless mic use.
Since you mentioned CB radios, that is an interesting history as well. As I understand it the situation was initially similar to GMRS radio today, the CB band was supposed to be for licensed users and you had a
call sign. In the '70's the abuse and misuse of the CB spectrum and associated regulations by users became so rampant that the FCC gave up on the licensing requirements. No matter how many unlicensed wireless mic users there are, I do not see that ever happening to the
VHF/
UHF spectrum without severe limitations, which is pretty much what the White Space or TVBD issue was all about.