They should. It's easy to report. Doesn't matter if nothing happens right away, because the more reports that accumulate the higher priority it becomes.
So instead of trying to tell me how fruitless this is and just give up to endless arguments, maybe report wage theft if you know about it. You can do it anonymously. You can do it for people that tell you. It's not a hopeless situation. Hell, lawyers take payment after the case is won, and you know if your wage is being stolen then others are too
It's easy to report, but retaliation is a thing, and is hard -- and expensive -- to prove. Someone subject to wage theft is not the kind of person who can afford that trouble.
And it's not like restaurant owners don't talk among themselves. Getting blackballed isn't great.
Bottom line is that you seem to think that there's zero reason why people are shy about reporting wage theft. And yet so many people don't want to do it. Maybe try a little humility on and accept that maybe there are reasons you don't know about or don't understand. It's very easy to tell people what they should be doing when you don't have to walk in their shoes.