I read an interview with a prosecuter (it may have been an AMA on reddit) where he said that while a lot of lawyers wanted to become defence lawyers because they dreamed of saving innocent people, as prosecutor he had the power to simply drop the charges, with no reason to go to trial.
The supposed obligation of a prosecutor is to seek justice, not to put people in jail. When the incentives favor injustice, they should be adjusted; public campaigns personally shaming overzealous prosecutors are one possible disincentive that could be added.
