Adena Farming - Why????

Hey all, this is my first post!

So I just finished reading "The Mangle of Play" article (Week 1.b) and the idea of Adena Farming came up. I understand that it is a form of job in the article and I think sometime last year I heard that players themselves actually pay Chinese to play and level up their characters in MMOGs.

So my (super long and repetitive) question is: Why would players from America PAY other people to level up their characters? Isn't the whole point of the game to obtain an accomplishment? I know I feel great when I level up my characters but I do that myself. But why would American players pay (in this case) Chinese to use their characters to level up? Doesn't that defeat the purpose of the game?

Confuzzled now...
Ju Mei