If you're picking up a trial account, chances are that you heard about it from a friend or a blog or a news report. But chances are, you were shown or described a massively armored warrior engaged in fierce hand to hand combat on the back of a dragon flying through the air, or a finely robed mage flinging a fireball at the face of the lord of all magic, or something similarly epic. With that in mind, it might justifably get discouraging to show up in game to find yourself dressed in rags, wielding a toothpick, and being sent to collect wolf pelts that inexplicably only drop off about half the wolves you kill.
With that in mind, it's easy to see how a trial account user could get bored pretty fast. But for me, there's one other angle that very few people seem to be bringing up: The social angle.