Kellogg Faculty Fellow Susan Blum is mentioned in an article by The Chronicle of Higher Education entitled "Cheat on Your Homework? In This Harvard Class, Just Say You’re Sorry." She explains how many professors are usually too busy with their own work so they prefer using their time personally helping students with questions, rather than documenting plagiarizing cases.
“We don’t tend to get any incentive for spending a lot of time dealing with student misconduct,” Blum said. “Is it worth my time going through the process? Almost certainly not.”