How many union members do you think experience wage theft?
Probably they could do a better job of advertising this to workers. Many workers experiencing wage theft probably are not aware of their options, and that's a problem. But when used, it works. I've seen it work.
As, often, do state labor authorities.
There are all kinds of de jure considerations that purport to protect workers, but they fail without an organization by and for workers to actually ensure they're enforced.
Well sometimes a truck is late, that's just the way the world works. In one of those cases, my boss asked us to stay at the plant an hour late; the truck driver was on the phone and said he'd be there shortly, but we had nothing to do but sit around on our asses twiddling our thumbs. One of my coworkers, more experienced than me, asked if we'd get paid while waiting. My account of the conversation that followed:
Boss: "Well uh, we're all just sitting here doing nothing so.."
Coworker: "The Deparment of Labor says..."
Boss: "WHOA WHOA WHOA! I was just kidding of course you'll get paid!"
Immediate backtrack. He turned on a dime as soon as he realized there were workers who knew their rights. I think information is the key. There is no substitute for workers knowing their rights.
How many union members do you think experience wage theft?
To substantiate and engage PR over abuse of workers by a corporation, the livelihood of individual workers who give witness to the allegations are at stake.
To substantiate and engage PR over abuse of the public weal, customers or the corporation by a union, usually no one's livelihood is threatened by giving witness.
It isn't surprising abuses by unions are easier to publicize and and more commonly substantiated. This dynamic will not change until workers have the equivalent of FU money. Or like in one sci-fi story I read, a genetic mutation causes everyone to fix chlorophyll in their pigmentation and get all their minimum bodily energy requirements by standing around in the sun for a few hours each day, and have to be convinced to work. I suspect a more near-term, practical direction is some solution along the lines of an intentional community co-op.