My theory would be that neoteny goes hand-in-hand with the traits of domestication (social friendliness, high tolerance of strangers, etc), and that humans are effectively self-domesticated.

Some of this is alluded to in https://en.wikipedia.org/wiki/Neoteny_in_humans which is a fascinating read, as is this very thread. Thanks for the food for thought!

I believe there's also a hypothesis that our ancestry back to the Devonian or Cambrian was based on neoteny/paedomorphism where a particular creature living on the sea floor, when in the infant stage, has a limb for propulsion which it loses when it finds a nice spot to settle. Our very distant ancestors didn't lose those limbs and evolved into the distant precursors to placaderms, bony fish, and, well, terrestrial fauna.