For the most part, those that are getting banned have used GPS spoofing or bots/automation to help themselves in the game, and Niantic isn't having it anymore.
The message gamers have been receiving:
Our goal is to provide a fair, fun and legitimate game experience for everyone. We will continue to work with all of you to improve the quality of the gameplay, including ongoing optimization and fine tuning of our anti-cheat system.
Written by: Andre Yoskowitz @ 13 Aug 2016 22:48