It’s a silly bit of theater and American exceptionalism.

Infamously, “grand juries” are supposed to be a check against bringing frivolous charges, but they’ve never done this: there’s a famous quote about a prosecutor being able to get a grand jury to indict a ham sandwich. They’re also used to kill trials which are politically inconvenient but which the government doesn’t want to take the blame for burying, usually for killer cops: just tell the grand jury not to indict and then say “welp, nothing we could do.”

All the romantic stories about jury nullification being a check against government overreach are also crap. Historically the most common use in practice, by far, was when juries would exonerate people who’d been caught dead-to-rights lynching black men.