Truth be told, I'm sure there were a few people using massive amounts of data (in the terabytes or even more) on AT&T's network using hotspots who ruined it for everyone.
Id love to know the single person responsible for the decision and why they even bothered thinking about these plans, I can't imagine there are that many.
Just on this forum alone there were at least a dozen people who were using at least 200gb/mo tethering.