One of my patients who worked for Verizon explained it to me. People who have Verizon can damn near use data in DWS when AT&T customers can't even get service on the old 3G network because of the minimal number of Verizon customers in there as compared to other carriers. Same reason you can't get on State's wi-fi on game day. The network becomes saturated. Now I haven't tried on LTE yet because last year I didn't have LTE service. That's also why more C Spire customers are complaining about their service now. They are approaching C Spire's limit on current infrastructure.
Also why a lot of stadium's are considering the installation of repeaters. Repeaters work to broadcast more bandwidth in certain areas where crowds can easily saturate coverage. I know that AT&T has space rented in DWS for future plans but as of last year Stricklin said AT&T had not approached State about installing repeaters. Auburn installed them before the 2013 season and several people said service was drastically better.
You're correct about why Verizon works due to them having fewer customers. That's also why Sprint can advertise the fastest network. They have no customers to load it down. Verizon in MS just happens to be a relative latecomer as opposed to AT&T and CSpire, so even though VZW has acquired some decent spectrum across the state by gobbling up smaller carriers, they still haven't made tremendous inroads to cut into the customers that have AT&T or CSpire.
Most of CSpire's problems on LTE have to do with the frequency bands they're using on LTE. They're presently using a higher frequency band to transmit their LTE, and higher frequencies don't transmit as far. Meanwhile they have 700 MHz spectrum as well, just like AT&T and Verizon, but the 700 MHz band that CSpire has suffers from interference issues due to being next to UHF channel 51, and nobody thus far has developed handsets that work on that band. That's supposed to be worked on in the next couple of years, and once they're able to deploy on that lower band, their LTE coverage should improve pretty dramatically.
As for the bit about the repeaters, I'm afraid that's just incorrect. Repeaters essentially rebroadcast existing capacity to make it cover a larger area. They don't actually increase capacity. You increase capacity by dividing the crowd up into smaller zones, where each zone has the same overall capacity. It's the adding-lanes-to-a-highway analogy, and that's the basis of what's been deployed at Davis Wade, Vaught-Hemingway, Bryant-Denny, you name it.