Public sector workers are notoriously less productive than private sector workers; its not surprising that a worker who is largely safe from being fired, is guaranteed raises every X amount of time regardless of productivity, and whose organization cannot be replaced would work less hard than a private sectory worker.
Public sector jobs usually offer excellent benefits that make up for the decreased pay. My ex-husband worked for a large county's IT department and while he made less than he could have made with a private employer, his benefits were unbelievable. Sick time, personal time, floating holidays, regular holidays, $800 a month to spend on a health insurance plan, etc. I understand that not all public sector jobs have those kind of benefits but the majority do.