About treasure maps...

So why are treasure maps still so limited?
I understand for the newest content, being limited to one map a day could make sense... But we have 4 different eras of maps now, why can I not gather an infinite supply of ARR zone maps... Or more realistically why cannot I gather one for each era per day.

As other content has expanded so has our limit on how much we can do. We have 12 custom deliveries and beast tribes now instead of just 6.

I know you can buy maps from other players so you can do as many as you can obtain... But why does it have to come to that for older content? if there were other ways to obtain the rare crafting materials that might be a solution, but they only come from maps... And as newer stuff comes out people will focus on getting the new maps and not so much the old. If we could gather one for each expansion era that would be more freeing.