Why are we not aware of the manipulation of our government by big business?

Your logic only goes so far. You conveniently ignored the fact that most Americans are a part of one special interest or another. Special interest groups are not limited to corporations. There are action groups, labor unions, and professional organizations , all with special interests that they lobby for. The two major parties win more often because they are the parties that deliver the most for the most groups. The other parties are mostly made up of those that are disappointed in the major parties for one reason or another. They do not get as much support, because they do not deliver.