The answer should be obvious. It is because we no longer live in a democracy or a democratic republic.
I realize that this is contrary to our programming. So, I'll explain it. A democratic government is one in which the people rule.
What is government other than making and enforcing rules?
So, who makes the rules?
So, who enforces the rules?
In any democracy, the people must have the power to enforce the law; otherwise, the people are ruled by an aristocracy which can enforce the law as they want.
In Britain and the U.S. before the fascist aristocracy regained power, any person could institute criminal charges against those whom he believed broke the law, just like in Ancient Athens, and if the majority of people on the grand jury thought that the charges showed probable cause that the law had been broken, the person bringing the charges could prosecute the defendant(s) before a trial jury or hire an attorney to do so or hope and pray that the public prosecutor would do so.
Justice Bradley also pointed out that if a person was deprived of the right to bring a criminal complaint to a grand jury that person was reduced from the status of a free citizen to no more than a slave. He stated, "To deprive a whole class of the community of this right, to refuse their evidence and their sworn complaints, is to brand them with a badge of slavery; is to expose them to wanton insults and fiendish assaults; is to leave their lives, their families, and their property unprotected by law. It gives unrestricted license and impunity to vindictive outlaws and felons to rush upon these helpless people and kill and slay them at will, as was done in this case." Id at 599.
Now, prosecutors stand as the gatekeepers keeping the ruling elite and their enforcers from having to answer for their crimes.
Before the fascist ruling elite took over the U.S., the facts and law would be argued before a jury of citizens who would determine whether or not the defendant(s) were guilty, and a guilty verdict had to be unanimous, an improvement over Athens where the majority ruled even at trial.
Yes, juries could nullify law in a democratic justice system because the people rule. Not guilty due to self-defense, duress, etc. came from jury verdicts, not legislatures. By the way, alcohol prohibition was repealed because it became nearly impossible for the government to win any conviction.
Now, contrary to the propaganda that we see on TV, judges routinely undermine the right to a trial by a jury of our peers, and judges, not normal citizens, make most of the decisions about who wins and loses in our "justice" system.
To restore the power to throw bad representatives out of office, the votes must be counted in public.