Rewards from low level areas at 80
I would imagine it’s more because there are no rare items at that level to give out in the loot tables (other than the odd crafting material).
If I remember correctly don’t rare items (as in weapons / armour etc.) only start to exist somewhere in the level 30-40 range, before then there doesn’t really seem to be any I have come across anyway. So I guess if the game determines that you have a rare drop it can only pick your current level to give you in a zone lower than this. Perhaps if you were say 80 in a level 50 zone it might give you a level 50 rare although I can’t confirm this and can’t remember if I have seen this happen or not.
I could be wrong, but I was wondering about this myself the other day when i was going through map completion.
I get a mixed bag of items in the area level range and in my level range, not sure about the rares, but I think WreckSC is right, they have a certain minimum level so you cannot have really low level yellows or oranges.