This is because the rate is calculated by excluding charges that were dropped by prosecutors, they only count dismissals and not guilty verdicts as losses.
Yes, you often see things like 99% conviction rate thrown around. 90% of cases end in plea deals anyway as most people aren't willing to use their right to trial because the time you get if you lose is often 10X what you can take on a plea deal. A vast majority of those found totally innocent through DNA evidence pled guilty to murder or rape even though they were factually innocent.
