Smear campaigns depend on the sympathy of outsiders. I can't smear anyone by myself, I smear them by convincing other people to believe negative things about the person I'm smearing.

If I can convince people to believe that someone accused me "falsely" by name and tried to ruin my career, I'm a lot more likely to gain the support of neutral outsiders against that person than if I go after someone who very carefully never named names.