The way you describe it though, it sounds pretty... disgusting... that grand juries nearly always indict. This would indicate that there is nearly no point in holding a trial if the norm is to always convict.
The same reasoning holds true for high rates of approval for warrants and 0% of airline luggage going through screening contaning bombs.
Trials are different because they have an extremely high standard - beyond a reasonable doubt. A prosecutor can be completely convinced in their own mind that someone is guilty of a crime and they have no choice but to bring them up on trial if they think they even have a chance of meeting the high standard, even though they may fail.
Indicting means proceeding to a trial.