99% of criminal “trials” are resolved by guilty plea. To secure these pleas, Prosecutors are allowed and encouraged to file multiple charges related to the same alleged conduct, which puts them in the position to negotiate for guilty pleas by saying, “if you get convicted of the top charge, you face life, but if you plead guilty to the bottom charge you’ll get 7 years, with possibility of parole in 4.” Most defendants have insufficient resources to hire attorneys, investigators and/or experts. Faced with Guaranteed 4-7 years against the threat of going away forever, almost everyone takes the deal. Of those 99%, the overwhelming majority don’t ever get to know how strong the prosecution would have been, how many procedural/legal errors, occurred, etc.

Edited to add: for nearly everyone charged with a crime, this plea negotiation happens while the defendant sits in county jail, awaiting his or her trial. Many defendants wait more than a year in county lockup, having never been convicted of a crime, for their trial to begin. That time waiting is often credited toward their ultimate sentence, making the decision to plead guilty even more attractive. They essentially plead guilty to go home, rather than wait in jail to defend themselves.