Kind of seconding everyone, their mother and the kitchen sink on the "Because I'm not in it to win, I'm in it for the fun/RP." Even as someone drawn to the magic class of every game he plays (Psychic, Warmage, Mage, etc.), I don't really like the amount of prep that the DnD prepared casting classes require. I'll play a sorcerer and still be effective by being a good generalist (or maybe thematic if being a sorcerer is a plot point). I'll play a Warmage and be great at throwing around damage right away with no forethought because that's the character. I remember playing a Mage during several runs in DA. Most effective one was a brutal debuffing, healing machine. However, I still needed the tanks to do damage while I ran away if things got ugly. It was fun, but I wasn't the only character on my team. Sometimes I want to play the guy who the Wizard is buffing instead.

Plus, as one of my friends put it: "I play a Crusader because at the lower levels, your prepared caster runs out of spells rather quickly, while I can keep smacking and recovering all day long." Especially to newer players, looking at a Wizard or a Sorcerer and seeing that they get, what, 4-6 spells a day at level 1, plus a small d4 hit dice (not an argument against a cleric, obviously), it's not encouraging to play at low levels, which some people forget is still played.