Because it's not good for the game.
Even without rhe 2xXP weekends, it's already way too easy to level in this game and there's really too many people that reach 50 without understanding how to play PvE in a group or do warzones. The more you simplifie leveling, the less people understand their class, their role and how to behave in a group.
That has nothing to do with how "easy" it is to level in this game. It has to do with the mentality of the player.
I have yet to play a game that I did not consider it "easy" to level up in. If I had found a game like what you describe when I first started playing MMO's back in 2005, I would not be playing them today. I'm not in to beating myself up and getting stuck with time sinks. I will stay with a game if it is fun, not if it takes forever to get a single character to max level.