So, stepping out of the ‘verse for a moment, why does paracausality exist?

Thematically speaking, the existence of paracausality says something very important about the nature of the universe. It means that it’s impossible to deny the existence of free will. (Or, rather, you can, but it’s about as useful as standing on a planet’s surface and denying the existence of gravity.)

You make choices, and your choices make you, and the universe you exist within. Create or destroy, heal or harm, save or damn, it’s all down to choice.

And either way, it’s your fault. No-one made you do it, not without rooting your brain and turning you into a non-volitional tool. Not society, not your parents, not circumstance, not culture, not memes, not instincts, not your friends, not your enemies, and certainly not the deterministic unfolding of acyclic causal graphs. Just you.

You chose, and the world responded. You did it. And the consequences are yours to own and to live with, forever and a day.

This gives the world a rather vital quality, especially in fiction: meaningfulness.