My wife and I were on the AT&T unlimited data plan which got grandfathered once they dropped that plan. AT&T was very interested in pushing people off of that plan which they achieved by throttling people who used too much data. My wife received notice that her data was going to be throttled for the remainder of the billing period for going over around 3 GB. This happened right around when T-Mobile started their "un-carrier" plan which included unlimited data, voice and text. We left AT&T shortly after and never looked back. Thanks to AT&T's shortsighted push to get people off of their unlimited plan, we found T-Mobile which has kept improving what it offers customers (we recently visited Canada and, thanks to their new plan which was added for a few dollars, we were able to use 4G
As long as AT&T and Verizon continue to treat their customers with contempt, people will continue to leave for greener pastures.