In NY it's because of the Taylor Law. Striking is illegal in the public sector. The union gets fined 2 days of dues for every day on strike so it is essentially bankrupted. Striking leaders and members are jailed. Like TWU Local 100 took a long time to recover from their strike in the mid aughts.

That being said nurses at Westchester Medical Center which is public and under the Taylor law won an 8% wage increase back in like September. So its possible.