Another reason is simple necessity. We needed a tank; I happen to be capable of doing the job and doing it well. Even back when threat was harder than it is now, I always knew I was a respectable tank. I pay attention to my positioning, I know how to use my cooldowns, and I've got a lot of experience with the role. When my guild found itself short a tank, it seemed like the right thing to do. It's just plain easier to recruit a DPSer and have someone established doing the tanking.
I've asked before if it's time to kill tanking. Almost a year down the road from that question, here I am tanking again. I think what I'm learning is that, at present, it's fairly easy to tank decently and not very hard to tank well, but tanking itself is now split into two halves, and one of them is actually more difficult than it has ever been. It's easier to learn but not easier to master.
Threat and the tank
See, threat is not a tremendous issue. The threat changes we've been living with for almost a year have made it much, much easier to hold threat even against very high DPS. Now, ludicrously high DPS can still pull threat, especially very early in a pull or on a mob that is annoying in its positioning (the charging adds on heroic Warmaster who can stay out of range of your threat moves for an annoyingly long time, for instance) or with constantly spawning adds that don't give you much time to build threat on them. It's not a major deal over the life of a fight, depending on the situation, but it can be irritating.
What I'm noticing in doing tune up 5-mans and Raid Finder groups is that, for whatever reason, people still do all the things that make tanking harder. They pull when you're not ready or not even close to them. They unload all their DPS right as you make contact with the mob or mobs. They play the go-go-go game. And while, thanks to the rather high amount of threat even a semi-competent tank can put out, they don't usually end up dying for any of it, it does make me wonder.
And since I've also played as a DPSer quite recently, I see the opposite side of the equation, all the bad tanking habits you need to make sure you don't pick up. Pulling so fast the healer is out of mana, being a condescending jerk, forgetting that there actually is a method to AoE tanking beyond spamming X AoE threat move. I even had to force myself not to pull a pack out of the group's AoE a few times, an old habit I developed from days tanking in Shadow Labyrinth back in The Burning Crusade when warrior AoE threat was pitiful.
The difference between tanking on the side from time to time to moving your focus from one role to the other on a semi-permanent basis is that it forces you to change your thinking. I always feel a sort of dislocation when I start DPSing after a time spent tanking and vice versa. To a degree, it forces me to relearn the class -- what the talents do, how to use specific abilities and not to use them, how to spec given different roles (Will I be add tanking? Will I be tanking a load of bloods? Will we be taunt-swapping a boss?) and what my experience with the fights as a DPSer allows me to be more or less aware of.
Frankly, DPSing causes me to develop a touch of tunnel vision, and tanking forces me to broaden out. I need to know if I'm in the right place, if I'm ranging the healers or not, what abilities are about to go off, if a debuff is stacking, and so on. It creates an entirely different experience.
Divided but not dissected
I said before that I believed tanking has become two separate halves. Frankly, it's not really new. It's just significantly more pronounced now. Threat is trivial to the point that I stepped back into tanking at the heroic level of Dragon Soul and didn't have a threat issue. I can tank a 5-man in my full tank set and never have to worry about things like taking off my pants to take more damage and thus generate more rage.
But while the threat responsibility of tanking basically just requires you to try and make an effort, the complexity of fights ranges from mildly difficult to quite hectic. Anyone who's tanked heroic Spine knows what I mean. As the fight goes on, you perform a kind of complex dance with an ever-increasing swarm of mobs that would like nothing better than to kill you. Over time, it goes from a slow waltz to a tarantella to a mosh pit, and while it's going on, you need to do more than get and hold threat. You need to stay alive, kite, use cooldowns to benefit the whole raid, and otherwise perform like a traffic director who is directing a school of sharks that want to eat him.
This isn't to say that tanking is super hard now, any more than DPS is, and certainly I believe healing to be significantly more unforgiving in terms of player error. Tanking has simply taken the emphasis away from holding threat and put it onto managing the fight. It's why I'm starting to believe that the active mitigation model for warriors could actually work in Mists, because it is philosophically what every tank is ultimately doing right now anyway. It just means we'll have more tools to do it.
My sojourn in the ranks of the DPS has allowed me to really experience the last week's return to tanking with fresh eyes. And in so doing, I've come to the conclusion that tanking's shift away from threat generation, although personally difficult for me to grasp instinctively (I was a threat tank, I was always working hard as I could for maximum threat), is a welcome development. Yes, people can still pull threat if they play badly, but now, you have a lot more of a chance to control that.
What you really have to work hard to perfect isn't how hard you can spam anything -- it's how well you can conduct the fight, how well you can stay alive, how well you can make the healers jobs easier, how deftly you manage the conditions of the encounter. You're not fighting your own group anymore in most cases, and it's a welcome change.
World of Warcraft: Cataclysm has destroyed Azeroth as we know it; nothing is the same! In WoW Insider's Guide to Cataclysm, you can find out everything you need to know about WoW's third expansion, from leveling up a new goblin or worgen to breaking news and strategies on endgame play.