Implied in your comment is that employees (assuming they are employable white collar employees) are empowered economic actors. They keep choosing to work there.
I think the reality of the employee-employer relationship is that employees don't have the sort of power, as one would have as a customer, for example. Part of the reasons are probably explainable economically. It's a fairly illiquid market for employees because the cost of getting to an agreement, negotiating terms (never-mind sampling) is very high. A lot of other reasons are probably best explained psychologically or anthropologically, roles we assume in certain situations. I suspect these are the bigger ones. Either way, barriers are there and bad treatment of employees often results in badly treated employees, not empty just resignations.
In a lot of ways, "if you don't like it, get another job" like "if you don't like it, get another country."
The free exchange economistic-ey forces are there, but they are not the only things there. Other things that make employers behave better is standards set by society. These are laws, but also just norms and practices. These are impacted by things like articles or consumer responses.
It's complicated.
I'm fairly sympathetic to a lot of libertarian positions. But, I don't buy into the strong economic rationalist arguments.
Economic forces dictate how some things play out. other times, other cultural forces take effect. When it comes to employee treatment, I think societal norms are a massive influence. The reaction you are observing is part a mechanism for this. Society's scolding amazon for treating its employees badly, defining and enforcing the nom..