They are constantly nerfing farming spots, so item hunting isn't any fun. Not to mention it is difficult to do it solo. And another note on items, there needs to be MORE! It is extremely easy to acquire forge armor, and that makes you just like every single other level 20. Nothing varies! The only variations are on runes, and anything over minors (excluding vigors) are worthless, due to the -health. Why is it that any expensive, cool upgrade has to have a negative effect that makes it lame? I.E. any vampiric upgrade. Woohoo, I popped one on my storm bow, and now I can't even run with it out, unless I want to be constantly healing myself. So there goes about 75% of the cool factor of storm bows. Weapons vary, but not by much. The variations on weapons once you get into higher priced items is hardly even noticeable, when one is actually out killing things. It has turned into a frenzy to see who can look the coolest. And what is with the matching armor only benefitting one element? Why would you want to buy a matching armor set, and have +60 armor to one element?
So playing past 20 would be beneficial to enhance your pvp character, but that brings up another mute point. PVP sucks! It is ridiculously boring... it lacks all of the aspects that make PVP in other games enjoyable. Limited trashtalking, and completely random opponents are an example. Who cares if you can beat a group of 4 people that the game randomly selects you to fight against? There is no bragging, rubbing in victories, etc. It is just boring. The gameplay stinks in pvp too, clicking on an opponent and hitting F1 F2 F3 F4 F5 is not something I look for in a game where I am challenging an opponent. Not to mention that most of your opponents will be equipped very similarly to you, and more varies on how strong of hits you randomly land than if your bow has 5% more damage over 50% health than the ranger in their groups. My personal opinion is that the only reason people play past 20 is because they have too much time invested in the game, and don't want to face the harsh reality that the game lacks fun.
Hell, I will even compare it to Diablo 2. One of the reasons that 50,000+ people STILL play diablo 2 is because of the items. Literally THOUSANDS of items exist, and the pvp is very entertaining. Not to mention the possibilities of building charcters to duel at different levels, which is impossible on GW due to the insta-20 pvp builds. Yeehaw! That is all.
Why did I spend fifty bucks and 74 hours playing this game?

EDIT: I won't even go into the subject of the rune trader.