The FBI, to its credit in a self-serving sort of way, rejects the routine use of the polygraph on its own people.
The only thing I ever withheld from the KGB were the names of two agents whom I personally had known and handled and had a particular feeling for.
The U.S. is, so far as I know, the only nation which places such extensive reliance on the polygraph. It has gotten us into a lot of trouble.
The use of the polygraph has done little more than create confusion, ambiguity and mistakes.
You might as well ask why a middle-aged man with no criminal record might put a paper bag over his head and rob a bank. I acted out of personal desperation.
Foreign Ministry guys don't become agents. Party officials, the Foreign Ministry nerds, tend not to volunteer to Western intelligence agencies.