Why Are More People Arrested Mean Less People Go to Prison?

The argument hinges on the theory that incarceration and arrest are distinct outcomes of policing, right? They're arguing that there's going to be more arrest, but that's okay because there will be less people in prison. Nowhere in this entire article have these two Harvard professors at any point considered the fact that when you arrest someone, they sometimes go to prison. It's not just like, it's not just wrong. People in this country die in between arrest and a fair trial.