In our society, we look at individual rights because we are an individualistic society. The United States has never been particularly inclined to see groups as groups rather than as multiple individuals (although we have looked at racial minorities that way).
By contrast, other countries like Mexico have been much more corporatist. There, society is much more organized by groups. The ruling political party was long made up of groups representing various parts of society (like unions). By contrast, American political parties are made up of individuals.
The only thing that I can attribute this to is individualism. The US has been built on the creed that people are responsible for themselves as indivduals. Therefore, we do not look at society in a corporatist way as some other countries do.