Because that's what happened the first time?

All we know and knew of Gelmorra is that after the Elementals had a hissy fit, people hid in underground tunnels until they asked "pretty please" and the Elementals let them build Gridania. We don't really know much else from Gelmorra past that. It required Edda and Nybeth to give it some further plot.
Also, this doesn't invalidate the Allagan bit whatsoever? Yes, it's "ugh" because how often are we going to recycle the same thing now? Are we cows that ruminate on the same food over and over?
And of course I would like to have more than just a tiny cutscene worth of things for lore. I'm well aware that Deep Dungeons are small snippets unlike massive content that go deep (pun definitely not intended) into the lore.
Again: the issue isn't them adding lore to anything. It never was for a second. You're being stubborn on this, when I've already made it quite clear. My issue is that they're defaulting to the same lore over and over, when you have other places that could do with a bit more, EVEN IF it's something small. Because the issue isn't quantity nor quality. It's how repetitive it's being.
I refuse to repeat myself any further. Either you understand this much, or you're just going to have to deal with it.