Because they can change the password afterwards. That step is not relevant, anyway. I just said it's favored.
Edit: You probably got me wrong. I don't need an account password, I just need the E-mail switched to mine. I got cheated like that once before, instead of recieving the account E-mail I got the pass. Made a shit char pro, pass changed.
Edit 2: I'm an idiot. I can see your point there (I can change the E-mail myself if I have password) Changing OP.
Edit 3: Omg, I'm a total dumbass. Could've changed the E-mail on the character I bought on the first Edit... QQ
Doesn't matter now, I guess...
Edit 4: Hahah, I remember what had happened! I tried to change pass, but it just sent him an E-mail about changing it... So yeah, my method of trading was 100% safe, I just forgot it was. I win. You lose.

"... and there, standing in confusion on the brink of defeat, Thilfing gave out a bellowing cry. In the shattering echo the Noms saw, as had been foretold, his pain, his agony, his anguish. His triumph."