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Polygraph examinations aren't admissible in that way. Otherwise crime would be as simple as pass/fail not-guilty/guilty.

This is why a (good) defense attorney advises you against taking a polygraph if one is offered during a trial. If you pass, the case is not magically dismissed: it's useless. If you fail, you aren't automatically convicted, but the jury has their view of you negatively influenced by your failure of the test. You have nothing to gain by taking and passing one in court, but you have an undefined jury sentiment to lose should you fail.

That’s only because they’re not considered to be a real lie detector in that context.

Isn't the jury view of you also negatively influenced by the refusal to take it, though?

That would not come into evidence as long as you have a minimally competent lawyer. The jury would never know.

Kind of like talking to the police. It can never help you and most likely will be used against you in court.

That's why polygraphs are not allowed as evidence in the courtroom.

The real problem isn't whether they are easy or hard to pass, it's that they're easy but people believe that they're hard.