I understand the tanking thing myself, and why I enjoy it is about the same. I play WoW myself, and have done all the roles, but the reason tank also sticks so well is its a lot of work to pull off to do well, but it also gives the most control over anything in my experience. The people need to listen to you or they are likely to get themselves killed, follow what the tank does and improvise over a mistake and you are set. From any other perspective, damage or heals, I can do so much less though, either taking the hit from a mistake one of us made, be it myself or the tank, or frantically trying to heal to no avail. At l;east as the tank I can try to control these mistakes, and the skill there comes from fixing it all before you wipe the group.