I think you're really out of touch with what is going on in the WISP space.
See the following product as an example:
14x14 beam-steering Massive Multi-User MIMO. This is able to talk, in the same channel, at the same time, to up to 7 endpoints using both vertical and horizontal polarities at the same time. Total throughput per 40Mhz channel: 1.2Gb/s per AP.
Because of the TDMA synchronization, you can actually hang two of these on the same tower front to back using the same channel. So 2.4Gb/s per Frequency. And there are dozens of channels available at this point.
Many WISPs are also using LTE hardware. In fact, most gear that WISPs use anymore has little resemblance to the "hang a Wifi radio on a tower" past of the WISP industry. They're all TDMA synchronization (since there is little possibility for a FDMA scheme in half-duplex channels), not CSMA like traditional wifi. They're all moving to various advanced modulations including multiple streams, spatial diversity, and a lot of other high-sophistication modulations to squeeze every bit out of the available bandwidth.
Note that by pointing this out I'm not arguing for a "WISP everywhere" model. Many WISPs operate a hybrid model, deploying FTTH where it makes economical sense to do so, and using WISP technology where it doesn't. It's not uncommon to find areas where it's 'miles per home passed' instead of 'homes passed per mile'. In these environments, it is not uncommon to see situations where the money spent deploying the fiber will never be paid back, even if 100% of the customer revenue is deployed strictly to pay for the fiber.