Why cant you unlock blood eleves on wow trial?

Answer 1

because when you get on the trial it's not the full game so you only have the standard things you can do on the game such as questing and customizing your character to your liking. Your not supposed to have everything a normal person who pays to play the game has. Your using the trial to figure out if you like the game or not, not to just get out of paying for it haha.