That's because their specific designs originated in version 1.0 where there was no glamour system, but for players any piece of gear could be equipped regardless of your class, with some very few exceptions such as AF - you were very severely penalized stat wise if you equipped something that was not 'reccomended' for your class or if the level requirement was less or more than six levels from your actual level/class rank however as the trade-off.
Hence NPCs like the Archons also appeared in weird gear combinations because it was reflective of what players could also do in that, that they retained mostly into ARR even after the redesign in 1.0 when gear started to become more restrictive for players after Jobs were added. And that continued into ARR even before glamour was added to the game.
Gender locks are a different barrel of moogles, and it really doesn't have anything to do with actual gender, and is just pragmatism - designing gear for both genders means extra modelling to cover both, and if they can get away with a piece of gear being gender specific, they can then use that time to do something else, theoretically.