The original report only analyzes successful exonerations. There are many times more cases out there of false convictions, victims who have not seen the light of day. Those without exculpatory evidence have basically no hope. Some of them have actual exculpatory evidence, but their appeals do not succeed.

Exculpatory evidence (evidence that proves innocence) brought up after a criminal trial was concluded often does not lead to exoneration. The burden of proof that is required to sustain the validity of said evidence is high, in order to disincentivize hiding evidence until after a trial is over in order to overturn the result. Exculpatory evidence is often thrown out on procedural grounds, even when the evidence itself is valid. Moreover, the criminal justice system as it operates today has little to no incentive to reopen cases, for a multitude of reasons.

Most successful exonerations require immense amounts of legal leg work on the part of lawyers, witnesses, and LEOs. Evidence loses value as time goes on. Most falsely convicted criminals have no resources to pursue their innocence. Even cases that seem like simple slam ducks, where a DNA test is all that is logically necessary to overturn the original conviction, take years or decades to complete.

"It is better that ten guilty persons escape than that one innocent suffer." - William Blackstone