The problem is that they're working on everything.
The 9 month retcon fiasco did NOT do anyone favors in making them look productive in the least, but as of right now, Riot is working on the lore and trying to get things done. Right now, they're trying to get some things concrete as well as work on random bits of the world that didn't have certain details or fleshed out more than "Champion A came from location A and oooh mystery."
And yes, there's still a lot of champs like that, but Riot is trying to get to them. they already did an overhaul of bios and character stories for most of the Shadow Isles caste which can lead to very interesting routes. MORDEKAISER's fucking castle is the foundation of NOXUS! Bleedin' NOXUS! We now have an anchor or roots which can lead to a story of how Noxus was founded (hell, we actually have story reasons for Mordekaiser to go to Noxus and meet any one of the Noxian champions)
But I digress. As of right now, they're working to certain points and while we have the plot hole of "We don't know what happened in this place, blah blah blah,"
they're working around certain parts, so when they do dive headlong, there won't be any plotholes in the writing.
Poppy has been around since Demacia's beginning--Since it's FOUNDING!
Sion's rework brought along with it necromancy, how he was resurrected, Swain's acquaintanceship with the Black Rose and LeBlanc (and Vladimir to boot, apparently.) Darkwill was assassinated, and Sion was the guy to kills J1. That's not Kalamanda, but they're giving us the friction that occurred between Demacia and Noxus in the past, the darkness Swain cloaks himself in, 2 stories that can lead to a full on explanation of the founding of two major kingdoms (Noxus and Demacia, though Demacia was half explained by Poppy's bio itself).
Now, while it's not the exact same story we know of before that has yet to be retold, they are still building around it to make sure that everything is in place.
TLDR;
They're getting to it.
Oh, and Ahri's bio seems to be timed around the Noxian invasion of Ionia
Jhin's VO suggests that he LIVED through it. (no, really. Check it out. They are honestly trying to get to that point)