Exactly what Hpelli said.
This is unfortunately common in lower end content, like normal and heroic dungeon queues, where massively overgeared tanks will just W key through the instance with no regard for the rest of the group.
Once you get into keystones, you see it way less. The tanks will still mass pull, but a good tank will bring them to a center position.
After a bit of practice, you’ll be able to identify where the tank is intending to pull them, and you can position yourself accordingly.
Also caster life in low content is awful. You typically can’t get off casts before stuff dies. Again, that goes away once you get into keystones, and they begin to feel like a real class again.