Just some personal thoughts.
1. People may choose this plan over a cheaper plan that offers the same or better options due to the coverage area.
Example being TMO while alright, simply cannot compete with Verizon in service here. ATT is up there, but still behind Verizon. In other parts of the country, like the very NE, Verizon and ATT reign king, and TMO is terrible.
2. TMO is cheap for a reason, not that they're passing their savings onto you. Their network coverage is poor in most areas and the bulk of their customer base are economically strained, for lack of a better descriptor. They make quite a bit of money on these poor sods.
3. Sprint's LTE service is terrible and their coverage area is tiny in most metro areas. TMO and Sprint cannot compete with Verizon or ATT in QoS here in this part of the country, neither can Metro PCS or what I presume was a Metro PCS promo pasted as an IMG on the first page of this thread. There is a resounding reason why Metro PCS is jokingly referred to as "Metro Piece of ****" in most places in the US where it's offered. They also deliver a QoS lower than TMO while being on the same network and use the same predatory behavior as their parent company in targetting foolish and impoverished individuals as their main customer base.
4. TMO and similar services love to dish out their sweet talk about how new things are or will be. Meanwhile ATT and Verizon plod along upgrading their network to handle more and more load. I can get full bar service in the middle of BFE, for lack of a more proper area description, hundreds of miles away from civilization, and still get service. Often as good as my SAT phone. Show me a TMO, Sprint or MPCS service doing the same.