Why are cosmetics so restrictive?

[Serilda]

You don't. Consider others. I am all up for tanks wearing bikinis and mages wearing Disciples of War gear, but a monk wearing the classic White Mage set can be confusing.

In terms of lore though, once our character has earned their WHM AF it makes no sense that they cannot continue to wear it while fishing, dancing at Gold Saucer or waving a sword around. They're still the same character; that's the theme of the game's job system. If people can cope with a gigantic metallic red pigman punching enemies as a Monk, I think they can cope with a really angry career WHM punching enemies as a Monk too.