The restriction has not been bypassed as it's about limiting how many you have per inventory type, not how many you have total.
Like I said, I believe the idea is about sharing. Even if only one person has all the maps, unless that person wants to go to the mail/retainers several times, they may distribute it to the rest of the party for convenience so that each member can have a chance to be the map owner.
And as for the economy, this also limits how many you can sell at one time, which has the benefit of letting different people get a chance at some easy profit.