The only slight nuance I'd add to that would be that it could actually be conscious, just not borne out of an explicit mandate or desire to rig.

It's kinda like in an office meeting, there are some people you're more willing to disagree with and others you tiptoe around, because of their personalities or situations within the company. And you're consciously aware that you're treating people differently, but you do it anyway because it's rational.

I'm just speculating, obviously, i dunno what goes on in refs' heads...