[spenczar5]

We don’t really know - you are right to ask this question. There are two methods and they disagree with each other. JWST is precise enough to rule out a simple reason like instrument imprecision.

So remaining possibilities are new physics, a deep flaw in our assumptions/methods, or a universe which is not uniform (but in a peculiar way).

[rainbowzootsuit]

Perhaps the small anisotropy that is observed in cosmic microwave background observations imprints to the dark energy that accelerates expansion. I haven't kept up on the modern state of the art.