Maybe because they're still building the world after the retcon?
You have to remember, the new lore post-retcon is still in its infancy. We just got Deamcia, Piltover, and Zaun fleshed out within the past year, with Bligewater, The Shadow Isles, and Mount Targon (kind of) before that. We still have Ionia, Noxus, and the Void to be fleshed out, along with all of the smaller, lesser known areas, such as the Kumungu Jungle, Bandle City, and the Voodoo Lands (if they still exist).
We still have champs that reference the Institute of War in their lore, even though it's been about 3 years since the retcon now. That number is slowly dwindling, but it's still there. Kayle, Morgana, Malphite, and Fiddlesticks just to name a couple.
All of this is being done while production on new champs and their stories is on going. Ornn is actually the first Freljord champ we've gotten since Braum, so, I fully expect quite a bit of Freljord lore to come with him. Not to mention VGU's, which not only come with basically a new champ, but also a revamp of that character's region. Yorick brought about the Shadow Iles, Galio brought about Demacia, Camille brought Piltover, Warwick brought Zaun (also Urgot), and Swain will most definitely bring about an update to Noxus.
Riot's lore team has put a monumental task ahead of them, and it's going to take time, especially if they want to do it right. We only have about half of Runeterra fleshed out into an acceptable state, and I'd say we won't see any significant amount of lore come out until after we have it all done, which may be several more years.
I know its hard to accept, but you have to be patient here. This is going to be a long journey, and you'll have to just wait it out.