Wage theft is the #1 fraud[0] in the US. So while the voluntary contract can be a win-win for a quite a few Americans it is still exploitative.
[0] https://www.epi.org/publication/employers-steal-billions-fro...
[0] https://www.epi.org/publication/employers-steal-billions-fro...
And that's only minimum wage workers, in a subset of the US.
Was there a particular reason you were under the impression that wage theft was uncommon?