Ezreal (The Champion) is the reason the League of Legends doesn't exist
So hear me out.
A lot of us were there when the Kalamanda Incident happened at the near end of the original lore with the League being an actual organization with a building and mages that basically controlled the entirety of Runeterra with politics. Not soon after the conflict and the arrest of Heywan Relivash and Ralston Farnsley, the lore began to shift away from that and our lore teams told us they were shifting away from the league and doing world based events and all that stuff.
Here's what really happened, though. When Zilean froze time over Kalamanda to prevent further conflict it put a lot of strain on the space time continuum. There are only a few characters with such a command of the very fabric of the universe, one of them being Ezreal. He's a confirmed time fugitive as referenced by Pulsefire Caitlyn. Assuming Pulsefire Ezreal is the same Ezreal from the original 'timeline' I believe there's an easy explanation for why we have no references to the League of Legends at all and how it's seemingly vanished from history.
Shortly after Zilean froze Kalamanda in stasis, I believe Ezreal managed to get a hold of an artifact that allows him to travel back and forth through time. Upon using it, Ezreal shattered the already strained timeline and caused a butterfly effect that erased the League of Legends from history. This Ezreal becomes Pulsefire Ezreal and his actions completely changing time as we know it is why Pulsefire Caitlyn and the Fixers are attempting to arrest him.
So there you have it. Ezreal broke everything.