This probably has to do with the historic split between 2G/3G technologies among the major cellular carriers in the US. In the US if you want or need true nationwide coverage (say you are selling a retail IoT device and your customers expect it to work nearly anywhere) you pretty much have to go with AT&T or Verzion and switching a 2G or 3G device between them is impossible. This gives those companies a lot of power to dictate to customers what technologies they can use with their networks.
Since LTE is the lowest common denominator technology between all carriers (and LTE is the only cellular technology with hardware that supports all cellular frequency bands in the US) the cellular market in the US is being pushed very strongly in an all-LTE direction. With the inclusion of Cat-M1 and Cat-NB1 modes in LTE release 13[0], LTE will soon be usable even for low-power IoT devices. AT&T and Verizon are already racing to support those standards on their networks.[1]
The mess that is US mobile protocols and frequencies is what makes me cringe when the rest of the world these days looks to USA for the "latest" in mobile.
Damn it, Nokia had a Symbian phone you could use as a basic desktop for emails and surfing back when iPhone and Android barely did video out (and had to kill the phone screen to do so at least on Android). The mobile world basically came to a standstill, if not went backwards almost a decade, because everyone turned to the odd duck out to lead them into the future...
Kinda weird too considering you can run GSM in the HSPA guard bands without a large degradation of HSPA performance.
Typically HSPA is 5mhz+5mhz FDMA, but the carrier is only 3.6mhz+3.6mhz and can be slimmed to 4.2mhzx4.2mhz on Ericsson equipment. NSN equipment can go as low as 3.8x3.8.
In a slim HSPA situation you can run multiple 0.2x0.2 GSM channels.
LTE I've seen all over deployed in 5mhzx5mhz, but I've never seen the 3mhzx3mhz or 1.4mhzx1.4mhz configurations in the wild (they would overload easy).
Sprint has 3x3 deployed on band 26 in some boundary areas of the ibez. There have been some sites spotted in Columbus, Ohio along the ibez boundary that are 3x3 instead of the 5x5 Sprint has deployed everywhere else that's not within 100 km of Canada or Mexico.
