AirFiber radios (I'm quite fond of mine) and other 24Ghz, 60Ghz, and 80Ghz radios have severe rain fade so you need to keep the distance down to one or two miles unless you feel lucky. Now find a cell tower in that distance with fiber and available mounting space. I suppose that isn't a big problem in a more densely populated area like southern California, but still more challenging than parking a 11Ghz dish on a rooftop somewhere within 14 mile or so.

From what I've heard most carrier interest in high frequency bands is for links going a few city blocks to connect micropops back to a area hub site. That kind of caution with fade margin is more in line of what I'd expect out of at&t or a similar provider.