Could it be possible that It's all Pulsefire Ezreal's Fault?
Basic idea: Old lore Ezreal eventually becomes Pulsefire Ezreal in the future. Goes back to stop a post-apoc future. Ends up forcing the timeline to diverge and create new timeline where Demacia is anti-magic, Varus is 3 guys in 1, Ekko exists, and Yorick looks cool now.
Maybe that's Why Pulsefire Caitlyn is after him? Some overseeing force over time sent her to chase him through time and stop him from changing the timeline further.
What do you guys think?