Why is there even a union vote? What is stopping some workers from banding together in a club, increasing their leveraging power as more choose to join?
Lack of legal recognition and protections? I'm not really aware of any states that have provisions to recognize a union that only comprises a quarter or a third of employees doing a specific job for an employer. Closest I've seen was places where different jobs were unionized and non-union positions, like one job where all the drivers got a union, but not any of the warehouse staff.