For good reason. Unions pool workers' interests against the opposing interests of the employer; which means for public unions, they go against the interests of the public at large. There are countless examples of this.
Naturally, in a country with a deep history of skepticism of centralized government authority, people don't view public-sector unions very favorably.
This feels contradictory to the sentiment in the preceding statement at first glance. If the people are generally skeptical of centralized government authority, why would they also be skeptical of unions who push back against that centralized authority, as opposed to seeing themselves as on the same side?
Or against the politicians / political class. And given the amount of gerrymandering that goes on in the US, whether the elected politicians actually accurately represent the public at large is debatable.
* https://en.wikipedia.org/wiki/REDMAP
See also "Teachers are now five times more likely to have a side gig than the average full-time worker":
* https://www.vox.com/policy-and-politics/2018/4/4/17164718/te...
* https://www.pewresearch.org/short-reads/2019/07/01/about-one...
Perhaps some public sector employees need unions because they're getting steam-rolled. (Of course some unions (e.g., police) may be too powerful.)
Some of that was possibly jealousy. But another factor is that unions for public-sector employees have always been more controversial in the United States than unionization in general.