Look at ANY game. Look at LIFE.
If something is easy to get, everyone will get it. And once they get it, they toss it aside easily.
I got Ashkandi after months and months of raiding; it was a symbol of achievement in both patience and ability. Still keep it in my bags at level 85. All that badge gear? Destroyed.
The actual leveling part of WoW is not very grindy, and the gearing part has gotten MUCH less so but you still need SOME because it teaches you how to play your character and work through your strengths/weaknesses. What if everyone had a max level max geared character of ever class? How boring would that be....
Everyone wants to get to max level in a week and gear up in just as much time, without realizing that is infinitely more boring in the long run.
Problem is, how do you make it 'difficult' without being 'grindy' outside of PvP, and still making it attainable for everyone with the dedication.