Fat Moogle Mount on Mogstation!

[Arrius]

yeah, because it is way more expensive for SE to make a mount account wide...

Technically, it is more expensive. They need extra data and traffic to check on your account and send over the mount to each existing character, and future ones to come.

It is the same with retainers - You 'rent' each month traffic and data from them in order for more storage space and retainer services.
They aren't Blizzard or Riot which can whip up their own server infrastructure. Extra traffic costs money, and it took them long enough to finally get the EU data center actually into europe.