The problem isn’t DNS traffic. The problem is that for years people have been using 1.1.1.1 in the configuration of software and devices when they didn’t have an up address to configure. The result is that when 1.1.1.1 becomes routable all that additional traffic flows there and AT&T along with other provides carries that traffic. I was wrong that AT&T was blocking it for honorable reasons but this is a still a significant amount of traffic.