It's the unintended consequences of good intentions. The belief is that the criminal justice system has been historically racist against certain minority groups. Once you've been to prison, it becomes dramatically harder to get a job and rent. So by being soft on crime they are righting a "wrong".

Noble intentions but it ultimate creates injustice for victims of the crime. It also promotes petty and organized crime. It also creates a cycle. Soft on crime cause a crime wave caused by social justice DAs. Voters get pissed and then only vote for Tough on Crime candidates. Tough on Crime candidates crack down on crime creating a sense of injustice. The sense of injustice pisses off Voters and they vote for Social Justice candidates who are soft on crime and the cycle repeats.

Jail is expensive and cities are cash strapped.