Right now the PvE content in this game is minimal, so I understand why so many people resort to PvP and Pking.
As for Luck i'm pretty sure they put it in there to prevent powerbuilds as has been said, I would like to see some cperks that are good use charisma too so we don't get the no brainer choice of 1 charisma for pvp.
At the moment the only real reason to take more than 1 char is for extra mercenaries or to talk to merchants, you can just make alt for merchants and the quests give out pathetic rewards and xp so not really worth doing them (except maybe 1 or 2 starting quest).