It's a poorly implemented system. Simple as that.

In FFXI Notorious Monsters were common enough that people were separated across the entire world, but each one only dropped specific items so you'd have to aim to kill the one which had what you were after. Since the hunt enemies in FFXIV all have the same basic reward, there's no distinction between one mob and another, so you get hordes of people trying to claim the same enemy all over Eorzea. Since there's relatively few zones and hunt enemies, this means every single fight is awash with players.

How they didn't see this coming is beyond me, or maybe they did, and didn't care. Either way, it's one of the dumbest systems they've implemented.