Well, you have to figure. Look at the entire game....It's huge. And realize that most of that content is only seen by your character once or twice over it's whole life for only a few minutes. The last, let's say, 10% of the game is "end game content" and that's where you are sitting.

Now I get that the grindy aspect isn't really fun. but until they start designing content that doesn't get "Outleveled" you're going to end up with it. But even when they do people will complain that they are reusing content. In the end, it really comes down to this.....
If one doesn't WANT to do something, they don't HAVE to do it. But one can't HAVE it if they aren't willing to PAY for it.