The way I see it -- and bear in mind, my vision isn't exactly 20/20 -- there are two chief motivators for those who raid. The first is a rather simple one -- they know the game, and they're going to play it. As real as Azeroth may seem at times, it is in the end simply a game to be enjoyed at its highest. For many, raiding fulfills that call. The allure of tackling impossible odds with nine or 24 of your friends in a stunning display of coordination is quite powerful and wholly compelling.
Yet on the other front, we have those who (like me) approach raiding not from a gameplay perspective but from a story perspective. Some see raiding as the way to conclude the story that we play through as we quest our way to the max level. After all, only by braving the Firelands is one afforded the opportunity to vanquish Ragnaros for good.
Why do you raid? Do you seek the thrill of downing a boss with your friends? Do you want to finally see that fiery menace destroyed for good? Or perhaps you are drawn by both possibilities -- to see the story to its end, and to do so with a group of your friends? Or do you prefer to wash your hands clean of the raiding scene, drawn neither by the cooperative efforts and payoff nor by the allure of the story's conclusions?