My union is a state level organization with excellent and calm leadership. There hasn't been a strike threat here in dozens of years.
Administration "fears" teachers in that they know there will be pushback coming if they don't execute changes fairly and with consideration. They don't have the privilege of handing down policies and then firing anyone who doesn't submit. Once they have the union's buy-in though, they can expect teachers to be not only compliant, but understanding and supportive of the change. It creates a better work environment.
It's also the strategy that most business and organizations use today, i.e. to get the input of those working on the front lines of an operation, not to hand down decrees blindly without the insight of the people doing the job.