Ok, but their responsibility is first and foremost to earn a living. It is the government's job to define and prevent exploitation.

I agree. And I have been in a position where I had to accept exploitation. But I also think that workers often have some agency, and to the extent they do they should use it to protect those who don’t. Examples would be saving enough money to quit in protest of poor treatment, or becoming particularly valuable to the company for the same reason.