Is there any reason Mysterious and Treasure maps are labeled as Unique?

[HEC]

They are unique so you don't can have more than 1 map each in your retainers/inventar and don't buy all maps in the MB in one go

That's a pretty moot reason as I can buy all of them anyway (only one by one) and simply moogle mail them to my friend(s). There is really no logical reason from the storage point of view to have them classed as unique. It's hassle with no benefits to anyone. They're already limit by 18 hr timer and classed as Hidden and that should be sufficient to control / limit the circulation.