Anti-farming?
I was out farming alongside some botters earlier to see what dropped off the mobs they were killing.
I definitely noticed a drop off in loot after about fifteen minutes (sadly, the loot was nothing special to begin with, but I was bored).
So it seems killing things over and over again for loot yields diminishing returns, forcing you to go kill different things over and over for loot.
“…we don’t expect you to be forced into dungeons at endgame.”
~ArenaNet
~ArenaNet