How do we know it's not happening? Or why would we believe it is happening you mean?
Why would we believe that an elaborate scheme to coerce people to use their share isn't happening? How does it go, the absence of evidence is the evidence of absence?

In some circumstances it can be safely assumed that if a certain event had occurred, evidence of it could be discovered by qualified investigators. In such circumstances it is perfectly reasonable to take the absence of proof of its occurrence as positive proof of its non-occurrence.