It's not about the "All Greed" rule. It's both the bloated loot tables AND the fact that a chest can contain two of the same item.
For example, if you beat the third boss in Void Ark, the following items drop:
Void Ark Belt of Casting
Void Ark Belt of Casting
Would it be reasonable for each chest to not have duplicates if the chest contents remain as big as they are?