This is all the explanation needed. You're asking why the tanks that aren't you won't put up with mistreatment like you do. The fastest way for a group to advance is to do so cohesively. On live we're overgeared and able to get away with a lot in instances. Sometimes the dps are so overgeared they can tank what they pull, my paly can. That is not always the case. It's not best practice for moving forward, and it might not be something the tank or healer wants to deal with.
A tank that lets a pulling dps die has done nothing worse than the dps has. Why get mad at one but not the other? If anything, the dps is at greater fault for actively endangering people and causing them stress while the tank simply allows people the consequences of their own actions. The tank is like a bus driver, responsible for the passengers, and you want them to smile while people are snatching at the wheel.
I'd argue they deserve a little space to dictate the speed. They bear the most weight in controlling the fight and in doing so they're taking on a job the majority of players patently do _not_ wanting to be doing at that time. There was a time that some dps classes were considered 'pullers.' Blizz has consistently pulled us away from that direction. They want the tank out front initiating and directing combat.