Second, the most productive subsidize the least productive, which essentially creates a similar free-rider problem that the compelled agency fees attempt to resolve. Those who receive the benefit of the negotiated wage but would receive less in a market environment are being subsidized by those who are more productive than their respective wage. In a sense, the least productive are free-riding off the most productive with an incentive to focus more on staying in the job rather than excelling in the job. This is a bit of a simplification, but the effect is there regardless.
Public sector jobs struggle to approximate equilibrium compared to their private sector counterparts, and in some instances, there are very few private sector jobs to compare wages against, such as public school jobs. Public sector unions tend to advocate pay structures which rely heavily on seniority and certain qualifications such as education. This is known as step-and-lane schedules. However, relying heavily on these two measures dismisses other relevant factors, such as quality of work, which may or may not correspond with seniority or education. Focusing on this type of pay structure, as advocated by public sector unions, tends to ignore more merit-focused alternatives and props up those who would thrive better under the step-and-lane scheme, such as those willing to endure a job rather than improve quality.