Prisons are packed because prosecutors are coercing plea deals. And, yes, it's totally legal.
“Though physical torture remains off limits, American prosecutors are equipped with a fearsome array of tools they can use to extract confessions and discourage people from exercising their right to a jury trial. These tools include charge-stacking (charging more or more serious crimes than the conduct really merits), legislatively-ordered mandatory-minimum sentences, pretrial detention with unaffordable bail, threats to investigate and indict friends or family members, and the so-called trial penalty — what the National Association of Criminal Defense Lawyers calls the “substantial difference between the sentence offered prior to trial versus the sentence a defendant receives after a trial.”“
NBC
August 8, 2019