Because it's literally the easiest outfit possible for it (and it's appropriate for the upcoming tenth annviersary).

The hint for all four parts is 'Where You Were Ten Years Ago' - it's literally your character race's starting armour (it doesn't even need to be dyed).

If you threw it away or discarded it, don't fall into the trap of buying a set from the Market Board for overinflated prices from opportunists, just go back to one of the three starting cities and buy a cheap set for 100 gil each from the relevant NPC vendor. Quick and easy.

I wonder what the next Fashion Reports will have as we get closer to the anniversary (and the Rising).