Note: This post takes place in a magical land before heirlooms, trivialized leveling, and faceroll AoE heroics. Imagine it as sometime in BC, when tank/healer leveling isn't trivial, but it's not the absolutely awful task of vanilla.
If you're smart like me, you rolled a tank. Or maybe a healer. We take the hard roles so the DPS can go off and frolic in fields until they get allergies and sneeze and laugh and go into shock and die. But it's okay, because they're just DPS.
I mean, it's a well-known fact that people generally have equal interest in all classes and roles, but that when DPS roll tanks or healers they are too stupid to handle it so they go back to DPS. If you were to watch the starting zones you'd see all these tanks and healers being created and if you track the names you'll see them get to around level 20 and suddenly blink out, only to reappear as a DPS.
Of course. It's simply a fact that most non-tanks/non-healers are too stupid to be tanks or healers. This is why DPS seem so stupid.
Or I wonder if possibly there's something else at play. Could it be that people are not born, or at least do not subscribe, as idiots? Maybe players are generally of around the same intellect. This doesn't fit my ego-boosting elitism, but let's play with this silly idea for a moment.
Let's take someone of equal motivation and intellect and split their fates into tank, healer, and DPS. Two strands go with the 'hard' roles while the other weaves its way through the 'easy' one.
Let's start with the healer. The first thing we should notice is that everything is the healer's fault. Short of someone jumping off a cliff, the healer could have healed better and saved them, and even with the cliff a priest could have use levitate and a paladin could have given hand of protection. Even if the group says nothing, the healer will know on some level that he could have done better, and it will gnaw at him. The only protection is either cynicism, not caring, or the careful balance of knowing exactly the limits of healing and when to blame others. This is why our normal person quit healing.
But let's say he keeps healing. Why is he so much smarter than DPS? Because he matters in the beginning and the end. He has to be on his game or that's it, game over, done. Being failure-adverse just like anyone else, the healer will learn to heal better, to watch better, to know more. He's not actually any smarter, but he is better educated.
Now for the tank. Given well-behaved DPS, he's going to be the puller. If he cannot pull properly, he will be first in line to die. Or maybe second after the healer. But his life is right on the line. He's up front. A DPS can run or feign, but not the tank. So he must watch and be careful at times. He must know where the patrols are, where to pull to, and possibly what abilities to watch out for. Failure-adverse just like the healer, he will learn and become better educated.
The DPS strand won't live the same way. He doesn't pull and he doesn't heal. His failures are slow and not always obvious. He has someone else to keep him alive. What is there to learn in this sanctuary? Very little. Sure, there is much to learn: kiting and interrupts and all manner of little tricks that one can use, but why? It would be as learning calculus in middle school. Sure, you can do it and it might even help, but all the tests are on long division and basic algebra. The normal person, not for lack of intellect, will not become well-educated as a DPS.
For an extreme example, imagine leveling a warrior vs. a hunter. The warrior takes all the hits and cannot heal. His escape options are limited, with all his mobility being focused on getting to enemies, not away. Short of intercepting a nearby critter, he's going to be dying where he fights. So he must learn to pull somewhat carefully. He fails, he dies. So he learns. Meanwhile the hunter is a melee class until level 10. At that point he gets a pet and with growl, autoshot, and feign death (admittedly not at level 10) he is set for the next 70 levels. Failure costs a piece of meat to feed an unhappy pet, not death. Failure is so trivial that it ceases to be a motivation to learn.
The hunter isn't stupid. The warrior isn't unusually smart either. Instead they are both players adapting to their situation. If the hunter had been harder to level, with risk of significant failure, then he would have learned more.
Notice how none of this requires any players to be innately stupid. It doesn't require that players flee from hard classes or roles. All it requires is that some classes or roles challenge the player or not. We know for certain that that condition is met. We have no measurement of player intelligence except biased, selective memory of incidents which may or may not be in any way related to intelligence. Given that we know that the education in WoW varies and that we cannot measure intelligence, wouldn't it be pretty damn stupid to assume that some players are stupid and ignore the teaching aspects of leveling?