Since ethics is the practice of knowing what actions are enriching and then doing these actions, anyone in business is tacitly bound by business ethics. The market is in many cases not a very effective enforcer of ethics because the public may not know about a problem until many years have past. By then, substantial damage may have been done. The company that caused the harm may have gone out of business. Think, for example, of the case of toxic waste pollution.
Employees working on the inside of a firm are in a better position to know what the firm is doing.
This insider knowledge creates a special fiduciary obligation binding employees. They are, in effect, the public's trustees. Like a trustee, they are morally required to consider and to act to promote the best interest of the larger community, the trustor. But there are greedy doctors and ministers, too, and no one contends that medical or ministerial ethics are mere oxymorons. Doctors treat sick patients who are not functioning at their best.