I really fucking hope that T-Mobile doesn't follow in AT&Ts footsteps with this one. This isn't just about old phones. With my Galaxy S5, I will sometimes force it into 2G only mode? "WHY?" might you ask. Well, let me tell ya somethin. Try going to PAX Prime/East, and look at how many high-end cell phones there are in such a small space, all being constantly used by tech savy and data hungry users. 3G/4G networks become extremely unreliable at events like this. However, practically nobody is on the 2G network. Yes, it is slow. But when all you need to do is push out SMS messages to meet up with friends in person, it is seriously a life saver.
Another reason is this. When traveling the country side, there are places that ONLY have 2G networks available, because they're literally in the middle of fucking nowhere. In rural America, 2G antennas are set to their maximum operating distance, because there are no other network towers to compete with. The "cells" become their maximum size. The furthest I've been away from a cell tower and still had 2G coverage was 20 miles up in the Rocky Mountains. These places are too difficult to run wiring to. Entire communities rely upon 2G connectivity for the most basic levels of outside communication, myself being one of them when I lived up there temporarily for a few months.
Good ol "PROGRESS"!