How so?
Because unions are a royal PITA for supervisors and management. They make doing business more tedious and difficult. They are just a legal "protection" scam that was invented by organized crime.
The same unions that run actual aporenticeships, pay a living wage, sued for a 40 hour workweek, and a retirement that offers a meaningful quality of life after your working career? Note! Not saying labor unions are perfect, but imagine only scab labor.