There are situations and situations, and as such, the Tank archetype is not a "catch all" archetype, like the GOD Wizard or CoDzillas. In fact, most of the characters that are going to fulfill this role are between tiers 3 and 5, and as such, cannot compete effectively with characters that have more options available to them - I.E tiers 1 and 2.
What is the purpose of a dedicated party tank, when the Wizard, Cleric and Druid can just summon one? Where the Psion can make a Lol Astral Construct? Or when all of them can freely switch between roles with Polymorph/Shapechange/Wildshape/Divine Power? IF the party already has reached the level in which these options become available to the T1/T2 classes, the Tank archetype loses it's usefulness.
The problem is, the Tank archetype is too feat intensive. At the very least, it requires Combat Reflexes, Improved Trip and Stand Still, and in fact, only reaches it's maximum effectiveness once you have acquired Robillar's Gambit, Karmic Strike, Defensive Sweep, etc... All of which are feats you'll only get far past the point in which T1 and T2 classes can do what you do - but better.
In a game where you have properly optimized T1 and T2 classes, a Tank is not required. That's not to say it's not useful. Even though the T1 and T2 classes can summon or become tanks themselves, they will not have all the range of options a PC that's playing a dedicated Tank has, nor will they have the specialized equipment to bolster that ability. But, then again, it's not like they NEED to, since they can pop up a Black Tentacles or Solid Fog spell and have instant BFC that's better than whatever a Tank has to offer.
And that's why the Tank archetype fails in D&D.
At early levels, you don't have the feats, items or number of attacks to be actually good in what you plan to do, and in later levels, you have the feats, but the Wizard/Cleric/Druid/Psion/Sorcerer/Artificer already has come past the point where most of his spells obviate the need for a dedicated Tank.
Now, in a game where you DON'T have T1 and T2 classes, then the Tank becomes relevant. In that specific situation, the Tank is fulfilling a role - that of BFC and Controller. And the other party members can focus on different roles, like damage dealing, buffing and utility, to round out the party, and defeat the encounters.
In fact, the same reasoning can be used for a number of other archetypes, like the Rogue TWF glass cannon, Ubercharger, etc...
In short, they are ALL very good builds, very good archetypes, that come very close to making a character a Tier 3. But because of the nature of the game, they cannot compete effectively with a T1/T2 character, because early on they don't have the tools, and later on, they are obviated by the T1/T2 classes. The role of BFC/Controller, which is what the Tank basically does, is a VERY important one, but it is traditionally fulfilled, in D&D, by Spells, Summons, Animal Companions or Polymorphed Casters - And they have such a massive support to do that, really nothing a PC can do can ever bring them close to the same effectiveness.