This is similar to many of my views on politics and government "conspiracies". I think its rare that its something overt and more often just how the incentives work in conjunction with human nature and desires. When you think about it, it would be much easier to address if it were actual conspiracies. Systems are much harder to change than to arrest a few bad apples.

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...