Are you sure they're actually guilty, and not just trying to get out of jail so that their lives don't fall apart?
Every part of the American justice system pushes people towards confessions:
a. People are sent to jail pre-trial. This automatically disrupts their lives, as even a few days in jail will often cost them their jobs. [1]
b. People can be kept in jail for months pre-trial, costing them their houses and possessions as well.
c. The government can freeze or seize a defendant's assets (effectively without cause), rendering them incapable of defending themselves. They can (and do) hold these assets hostage to coerce a confession. Thankfully, the worst of these practices have been struck down recently [2]
d. Being unable to pay for your own defense lawyer gives you at best an overburdened public defender (poor defense), and at worst no legal representation whatsoever (no defense) [3]
e. Bail eliminates the only remaining way to avoid jail for the poor or those with frozen/seized assets [4]
f. Overly harsh penalties make it too easy to completely destroy someone's life forever. Even 10 years is ridiculously high, especially considering there's no path to reintegration into society in America. You're pushed outside and left, destitute, to your own devices. It's far preferable to start with a scarlet letter now than in x years, older, less employable, with zero assets.
g. Plea deals, while well intentioned, have become de-facto extortion due to the other problems in the American system. "Take the deal or else we'll keep you in jail, and maybe even tack on a bunch of extra charges to keep you here for decades". Even without this problem, plea deals are a corruption of justice. Either someone is guilty and deserves the punishment, or they don't.
A conviction rate above 80% is automatically suspicious, simply because no police department is that efficient. America's conviction rate rose from 75% in 1972, to 93% in 2012, and is still rising. Couple that with an incarceration rate rivaled only by authoritarian regimes, and I'm VERY suspicious of statements like "90% of defendants are guilty".
[1]
https://www.americasquarterly.org/aborn-prisons
[2]
http://www.abajournal.com/magazine/article/court_says_crimin...
[3]
https://www.cbsnews.com/news/inside-new-orleans-public-defen...
[4]
https://eu.tallahassee.com/story/news/2018/08/23/federal-jud...
https://eu.usatoday.com/story/opinion/policing/spotlight/201...