The employer might have had practically unlimited resources in terms of money but it did not have unlimited resources in terms of qualified air traffic controll

The employer might have had practically unlimited resources in terms of money but it did not have unlimited resources in terms of qualified air traffic controllers and this is where the leverage normally is. Replacing employees in most jobs has a cost and so strikes hope to leverage an economic cost/benefit analysis as well as public & media sympathy. In this case anti-union ideology overrode the cost/benefit of this strike. It sounds like proper staffing levels for air traffic controllers weren't restored for about 10 years, so there was a substantial cost.