The sources of differences in ethics between people, companies, and nations.
Since you have tagged your question with health, I will approach it from the medical ethics angle.
Cultural factors have a strong influence on people's views of the value of life and the meaning of death. In cultures where reincarnation is a common belief, death is not viewed as an outcome to be avoided at all costs, whereas cultures that believe that each individual lives only once may make much greater efforts to avoid or put off death. These two opposing approaches affect the availability of critical care, life support, and resuscitation. They may also affect when and how vigorously an individual seeks treatment for various maladies.
Another factor is the cultural view of human equality, or lack of it. In some societies certain classes of people are viewed as being of less value than members of other groups. In a situation like this, those lower class members - be it women, people of a lower caste, people of a minority religion, or prisoners - may not bee seen as entitled to the same standards of care.
For corporations, the sole objective is to make money. A company needs to prioritize its activities in order to do this. If individuals and their doctors are willing to pay for a drug or service, then companies will be able to provide it profitably, and will endeavor to do so. Whether a company acts ethically is to some extent in the eye of the beholder, as is evidenced by the debate in the US over animal testing. Testing medical products on animals was commonly accepted for decades, but public sentiment has changed, and companies are now being pressured to find alternatives to animal testing; doing so may be the difference between being profitable and going out of business.
So the way that I can understand is the differences between the ethics of people, companies and nations.... is that the people ethics is like looking at the belief of their cultural. Because it is like a church you have all the different churchs. One Church have this belief and another has another belief.
For the companies, to who can make the most money. The company put there heads together to see what kind of money making ideals they can come up with.
For the nation, it is to put people in to groups like the poor, middle class and the rich. The one's they look at the most are the rich and that is not right.