How could I have better predicted this? I remain at a loss.

It's not a good answer, but statistics. Currently you have something like

• "there are criteria for accepting or rejecting beliefs, this belief fails the criteria, people won't believe it". That in turn relies on either
• "I have criteria, most people are like me, most people have criteria" or
• "criteria for accepting/rejecting is fundamental to human brain". It also relies on
• "I think this belief fails the criteria; my thought process here is not atypical" and
• "my model of the criteria is correct".

Whereas statistics are simply a description of what people believe.

But that hardly addresses the cause.