An explanation of aetherytes, the teleport spell and the return spell, straight from the localization team:
https://forum.square-enix.com/ffxiv/...An-aether-what
The limit, lorewise at least, is from the spiritual energy known as anima. The WoL has so much of this energy that they can basically use teleport as much as they like, but most people are not so lucky and cannot use it to travel as far or as often.
It used to be an actual gameplay limit in 1.0, with anima as a naturally regenerating resource that you used to cast teleport. AFAIK you could run out of it entirely and be left unable to teleport, the whole thing sounds pretty annoying and replacing it with using gil was almost certainly for the best, even if the whole
'good guy WoL leaves a small pile of gil at the base of long abandoned aetherytes' "lore" is a bit flimsy.