They are not admissible in court because they are not very reliable by themselves. It is way too easy to get a false positive result (subject concealing something) from a nervous subject.
That does not matter very much if the only consequence is throwing out another job applicant. It is much more serious if the consequences are being fired or going to jail.
I have taken polygraph exams as a requirement for a government contract. I passed, of course. The trick? I was relaxed, confident, and did not have any of the adverse activities in my background for which they were looking. Easy.
It occurred to me that a trained sociopath or natural psychopath could easily beat a polygraph test, no matter what was in their background. They would either believe the lies they were telling, or they simply would not care enough to show any reaction that could be measured by the machine. Certain drugs could probably mask or distort the biometrics to the point where the operator could not interpret them correctly.
They asked a question during the interview: "Are you using any drugs or other countermeasures to alter your responses to questions?" It must be a sore point.
Why would anyone bother to subject Hunter to a polygraph anyway? With his known drug habits, I expect that the biometric readings from such a test would cause the operators to walk away mumbling curses.
Got polygraphed once. In between questions I got a head rush, and practically sent ink stripes up the wall. Didn’t get the job, but on reflection it was probably a blessing.