There's often differences between benefits for individuals vs benefits for the organization as a whole. If more people got fired so the remaining teachers could

There's often differences between benefits for individuals vs benefits for the organization as a whole. If more people got fired so the remaining teachers could get paid more, the organization would be weaker while many of the individuals would benefit. Teachers (like everyone) tend to think of themselves as "above average" so no one thinks they'll be the one to be getting fired. Union officials place priority on the organization, and not the individual.