Except.....it's not changing? Or it is, just not in the way you think.
Riot is still working through their retcon they did a few years back. There are still plenty of champs who are intrinsically linked to the now non-existent Institute of War. It only feels like the lore is constantly changing because they keep on updating the champs and regions from the retcon. Once we have all of the old lore out, you'll start to see a far more streamlined story.
Just look at how well fleshed out Shurima, Piltover, Zaun, Mount Targon, Bilgewater, and the Shadow Isles are now. Thanks to Galio, Demacia is now far more fleshed out than it was, and I am certain Noxus will get a massive update once Swain's VGU hits.
Ionia is still kind of a gray area, but slowly getting more fleshed out with every passing week. The Freljord had a nice foundation laid down all the way back during Lissandra's release, but since that was before the retcon, and, frankly, still when the Journal's of Justice were still coming out, it could do with a little more work.....something we got to see with Ornn. There are also other minor areas that have yet to get updated/removed such as the Kumungu Jungles, and the Voodoo lands (those may very well get removed entirely, since only Annie's lore references them).
So, yes, the lore is constantly changing, but it's changing into a far more fleshed out, and complete experience......if that makes sense.