You asked why and I explained it to you.  You asked about a polygraph examination, not a standard police interview/interrogation.  They are two completely different processes.  Don’t try to change the substance of the original question.

Those are my rules and I explained why.  I’m sure other examiners have similar rules.  My rules are not open for discussion or negotiation.  We are not there to debate in the pre-test how accurate the test is with the attorney.  That is interference with the matter at hand.  It will not be tolerated and can be disadvantageous to the attorney’s client.  Smart lawyers are aware of that.  If the client or lawyer do not like the rules, they may go on their merry way.  

Maybe I wasn’t clear.  I do not interview the client at the end of the test when the test is administered to an examinee who is represented by a defense attorney and when the defense attorney requests the test.  The test results help the defense attorney, regardless of the results.  Your question has been answered.