The bitrate is a huge deal. High costs on the backend are a legitimate concern, but ultimately we've got a finite number of base stations and some areas simply

The bitrate is a huge deal. High costs on the backend are a legitimate concern, but ultimately we've got a finite number of base stations and some areas simply will not get base stations, ever. SMS is probably the only protocol that can extend any amount of coverage into these remote areas where message delivery can be a matter of life or death. And some of these areas aren't even that remote, just unintentionally RF shielded.