How could you possibly know enough to base assumptions of what anyone else finds fun? Especially when you are pretty much talking about a game that has over 7 million players. So...they all are just doing something they hate?
Your argument also fails to realize that achieving on it's own is fun. So what if the road there (grinding rep or doing dailies) is not fun if at the end when you receive what you were after you feel accomplished? How is grinding out a specific set of dungeon gear in GW2 any different? Oh ..that's right they don't have reputations...rather they just have unique currencies linked to each dungeon. How is that any different?
Why do you think people get titles like 'Loremaster' or 'The Insane'? I doubt they had fun doing every single quest as if it were the holy grail of gaming, and I doubt they had complete bliss grinding all those different reps...However I am pretty confident they feel accomplished and happy when they finally achieve that goal. That's how games work. The way you describe it kind of feels like you are telling us we shouldn't have any goals or anything..we should just run around giggling 'la di da di da' having "fun" because there are pretty colors in front of our face.