It's a technical/commercial necessity to have exclusive use over the spectrum in a given area. If you don't believe me why doesn't every city in the world have a paid wifi network? With 5Ghz it should be faster than typical 4G/5G speeds, and it only needs lampost level APs, pretty similar to the microcells that carriers deploy but an order of magnitude cheaper. Instead mobile carriers would rather buy 3 or 6ghz spectrum that only ever gets used in cities anyway, why not wifi in the cities?
ISM is tragedy of the commons; make it free, let anyone do anything and it becomes junk. Carriers need something they have exclusive use of.
ISM is thriving, the only tragedy is that carriers haven't figured out how to charge rents on it and that's a tragedy for them, it's a spectacular success for everyone using it for free.
Carriers don't need 6GHz for backhaul. They have fiber and cable and (other) microwave. Not to mention the ability to shape their own links with antennas and beam forming and do a good job of it rather than a "default job." What they don't have -- and shouldn't be given under any circumstances -- is the excuse to build a moat in the bustling public park.
At the very least, I don't see a need to grant exclusivity across an entire country. e.g. from my home, I can see 5 wifi networks including mine. Of those, only 1 other than mine has a 5GHz signal that reaches me, and everything other than mine is in the -80 to -95 dBm range. There's simply no need to reserve short-range signals in the suburbs in the way that there is for block of giant apartment buildings each with 100s of networks on top of each other.
On top of that, mobile data is quite expensive in the US, so the only time I have data when out and about is... when I'm on free public wifi networks (which is most of the time). So I don't see much reason to give more of a monopoly to mobile providers. I honestly don't even see a use-case for cell service outside of super rural areas; the only reason I even have it is because it's necessary for MFA. Cell providers are legacy tech as far as cities are concerned IMO.
To me it'd make way more sense to me to let wifi have more bands with stricter limits on power levels, and any exclusivity should be to municipalities who can contract with companies to build and manage their infrastructure.
I certainly agree about regional licensing. I think the best scenario would actually be to allow some for WiFi and some for carriers, especially since selling licenses is a two way door in a way that ISM isn't.
ISM is tragedy of the commons; make it free, let anyone do anything and it becomes junk. Carriers need something they have exclusive use of.