Is there a lore reason for why we can fall from great heights?

[Shori]

Interestingly, up until ... the start of Stormblood, I want to say ... you DID take massive fall damage in dungeons.
The Aery and Hullbreaker Isle being the most notable I remember.
It still could not be fatal, since both were in spots where it was impossible to already have aggro.

Quoting so that I can say your bunny is cute. Good job on it.

But also on related note: there was a change implemented around mid-ARR maybe on the run up to HW where you dont die if you meet two criteria: no aggro, full HP or survivable HP. I dont know if its still the case but Rogue/Ninjas have an unlockable trait that increases their fall tolerance. So, whatever part of the rogue questline explains that extra tolerance might be a hint at why you now no longer die from fall in dungeons