If you only "balance" a class by limiting its number you will lose alot of customers and create alot of funny forums threads. If there are like 5% jedi´s only but those can beat the crap out of any mix of classes up to lets say 5 or 6 players quite alot of people will turn their backs to that game. Its no fun when you lose to someone just because he was the lucky guy to get to play the most powerfull class.
And MMO´s are not about what the hardcore player demands lore and balancewise, they are mainly about getting as many subscribers as possible.
And there is no way a company would sacrifice the largest part of their community, the casual gamers, those who never play more than a few hours per week (therefore use up the smallest amount of resources but pay the same amount of money) just because they wanted to stick to the lore