Because it costs each innocent victim tens of thousands of dollars to defend themselves. If they are poor, they may have no defense. Next, they are plea bargaining to a crime they didn’t commit because that is the only reasonable option left.
How does this exonerate him if he has no lawyer to go thru the procedural efforts? You are right that hiring a lawyer is a choice, in as much as going to prison is a choice.
Because police would likely not even contact him in the first place once they see that there's nothing extraordinary about his movements.