Vanity Clothes

[Esmian]

Not all npc's in limsa who wear it are prostitutes. There's a Roe lady in the markets who wears it, she's just shopping. There's one npc who wanders around the bismarch that wears it as well. The dress is more of a casual dress. Just happens that yes, a lot of the ones wearing it are flirty. But this is a pirate city after all.

All NPCs in Limsa are prostitutes. Especially the prostitutes.

[Araeya]

Besides being a time/gil sink, it likely was intended to rejuvenate high level crafting, as well. Before 2.2, high end crafting just wasn't very valuable anymore. Now it will be again, at least for a time.