I went PvP for many reasons. Which I will list for you :P

I just got burned out on my Warlock in Sunwell.
I've wanted to roll another shaman for a long while (was my first class, on an account that I lost )
Ellay is so damn sexy.
I enjoy PvP very much, but both my warlock and priest are full S3 and maxed so I only really log on them for the weekend games, and thats it.
I like to beat other people, in what ever game or aspect of life, I am very competitive.
Plus as much as it is nice to copy something so great as ellay, I also think that if you really stop and think about it, (s)he? picked the best class for a starter multiboxer, plus shamans are the one class that stacks best with it's self. Not to mention they are great for pvp and pve. Plus they can heal and DPS.... you can't get a better class. And pvp with shamans is just so full of win...

Theres many more, but those are the main.