To emphasise killing monsters for your own loot. In reality, getting X item to trade for Y item is a symptome of "I never see X item". It is not a direct feature in any sort of manner more so then a solution to a problem with drop rates.Quote from EntyWhy put in BoA and completely ruin trading and any sort of economy?
And that is now being fixed with drop rates. Beyond this, they do not completely ruin trading. You can still trade with ppl who you actually PLAY WITH, IN A GAME, where they get their drops. God forbid that you actually have to participate in the kill to get that loot right? It's like you actually have to.. you know.. play the game. Heresy.