For at least some of us, warrior was the class we rolled because we played Barbarians in Diablo 2 or Fighters in D&D or what have you. We didn't know much about this game, and warriors seemed like the easiest class to get a grasp on: they were the ones who ran around hitting things. (I'm well aware that neither of those classes is that simple, but man, we want this thing to end someday, right? I mean, I enjoy things like food, sunshine and my wife's company, and I'm sure you enjoy the first two. You'd better not be trying to enjoy my wife's company, though. She'd bludgeon you to death with your own limbs. This is part of why I love her so much, she makes wolverines look like lolcats.)
I'm sure not a few of us, when starting out, rolled our warriors based on little or no experience with the game. Some came from other MMO's and thus had a grasp of the basic mechanics of gameplay they could be expecting, and for them choosing a warrior probably meant more deliberation than for others. For myself, I started gameplay with absolutely no idea what I was doing, and I started off with a paladin because I liked the idea of a holy warrior, but I quickly gravitated to the warrior class. I didn't like it for the first three levels, and then something magical happened.
Charge may well be the single most fun ability in the game. It's not tremendously powerful if you think about it, but what it lacks in power it makes up for in sheer coolness, and I've never played another toon without missing it. It's so breathtakingly simple and yet almost impossible to tire of using it. Just push a button and unleash hell upon your enemy! Crash into him, stunning him, and begin your assault. Charge is gained at exactly the moment where a fledgling warrior starts to realize that for his higher armor he's actually a good deal more fragile than other players, because if he starts a fight and it goes against him, he really can't do anything about it. (Admittedly, at level 3, you're not fighting anything hard.) But just as the monotony of auto attack and Heroic Strike is starting to get to you, here comes charge and I was hooked.
I think the transition into charge, a powerful yet simple ability that has more ramification than you would expect, helps sum up the warrior class to some degree as well. Warriors are, on the surface, a simple class. You wear the heaviest armor, get the best weapons you can, and you hit things. There's no worry about mana conservation, no complicated seal/aura or pet management system, you're not dropping totems or worrying about sneaking up behind things and juggling combo points. Like the humble grunt and valiant footman, it looks easy on first glance.
But the more you play the more facets open up to you. You begin learning the stances, and how to manage them. Some abilities work in all stances, but others do not, teaching you to dance between stances to accomplish your obectives. The easiest way to tell someone who plays the warrior as his 'main', so to speak, versus someone who plays a warrior as a vacation and hasn't begun to grok the class yet is by watching him or her in combat. Does he stance dance when it is necessary or does he plop himself in a stance and stay there? Stance management is key to the class and unlocking its more strategic aspects: many who believe that all a warrior has to do is run up to them with a big 2h and cave in their skull with a massive crit have no idea at all about how carefully that warrior had to manage his abilities to stay alive long enough to get in there and get the chance.
Likewise, as warriors begin to tank they begin to learn the threat management system that is, in my opinion, one of the most versatile and flexible tanking methods in the game and also one of the hardest to use properly, requiring the most attention and concentration if you intend to use it to its fullest. Anyone can run in and spam sunder, yes, but to truly unlock the system and its many options you need not only to spec higher up the prot tree to learn them, you need to develop a keen situational attention and grow comfortable with your abilities. Warrior tanking is hard, yes, and it may be harder for a warrior to generate aggro than it is for other tanks. It's surely the case that to maintain aggro a warrior needs to be paying attention to the battle. But with abilities like Shield Block and Revenge, Taunt, Sunder Armor, Heroic Strike, Rend, Thunder Clap, Demoralizing Shout, Challenging Shout, Commanding Shout, Shield Slam, Shield Bash, Spell Reflection, Intervene... the warrior's tanking palette is probably the most varied of all current tanks, with options for increasing your own survivability, reclaiming hate and reducing the enemy's ability to do damage as well as turning that damage back on them.
It is as always pointless to argue about who the 'best' tanks are. The best tank will always be the tank who works the hardest to hold aggro and stay alive. But warriors are, to my eyes, the most engaging and variable tanks, with the widest assortment of abilities aimed at all the aspects of tanking from survivability to hate management to enemy debuff. Not perfect, and perhaps in need of a few tweaks, but once you grow accustomed to the state of mind a warrior tank requires you'll swear by it: tanking on my paladin now is painfully boring and mana dependent compared to my warriors.
Likewise, warrior PvP and DPS are on the surface very simple and easy to grasp, but are remarkably variable and complicated once you begin to apply effort into mastering them. It's not just finding the biggest 2h you can, or the right combination of fast and slow for dual wielding... if a warrior wants to top the DPS charts he'll need to know how to use abilities like Piercing Howl and Heroic Stike in tandem on dazeable mobs, he'll need to know how to throttle his damage and threat (the days of Heroic Strike spam to maximize DPS are, if not death, certainly much less prominent now), and how to adjust his role on the fly. It's not fair to say that other classes don't have their own complexities, but finding the complexity of the warrior class is a moment of clarity, of seeing a flower unfurl before you or feeling gears mesh perfectly in your head. It's when the class really becomes your class, and it's part of the addictive nature of playing a warrior in my opinion. The more performance you can squeeze out in PvE, and the better you get at staying alive long enough to deal damage in PvP, the more you grow to love the endless cycle of simplicity and complexity being a warrior can offer you. I still remember the first time someone explained to me the concept of a rage dump, as I'd leveled my warrior back before patch 1.3 when they fixed a lot of really annoying things that kept us starved for rage. Ah, patch 1.3, you understood me when no one else did. Call me sometime, we'll run Dire Maul.
In the end of course none of the classes in the game can be summed up so easily, and the warrior is no exception. Whether you're a tank laughing in the teeth of a dragon or dodging the tentacles of a monstrous god, a brute wading into the fray with a hammer or axe as big as you are crashing down from your punishing grip, or a frothing madman swinging two swords around while the haze of hate overwhelms you and sends surges of power down your arms, the warrior as a class has as many reasons to play it as there are players who choose to... and that's quite a few, despite all the 'don't have' and 'can't do' you can list. Clearly, what we do have and what we can do is compelling for many.
What about you? Why do you war?