6 years ago, both Tmo and Verizon had big corporate-image ad campaigns. Those are the kind of ads that don't sell a specific product as much as they sell the company. Verizon had their memorable "Verizon network" ads, that trumpeted the reliability of the nationwide Verizon network, and showed an army of technicians prepared to stand behind it. T-Mobile had somewhat goofy commercials explaining their "Faves" feature, which was unique at the time.
6 years later, Verizon is still reaping the rewards of those memorable, well-targeted ads. Of course, it does help that they really do have superior network coverage, if not necessarily superior reliability.
And what of Tmo? Not 2 years later, they abruptly discontinued the Faves program. They still have no consistent corporate them, other than, maybe a vague sense that they are cheaper. The coulda been the Android carrier.