The fact that work visas are tied to a concrete employer is the biggest slavery scam the US is pulling off.
This, in an era when we're editing flowcharts, technical documents and schematic diagrams to avoid potentially offensive "master/slave" nomenclature.
Which is not comparable to having to leave the country you live in and possibly have started a family in because you change employers.
Sure, being tied to your current employer in a way that makes it hard leave is a terrible position to be in, but these folks are also well-compensated workers living comfortably in the richest nation on earth. They're free to travel anywhere in the US and are free to leave their job at any time.
Actual slaves don't spend weekends wine-tasting in Napa or cutting work early to catch a Giants game.