What is the sense of auditing the wealthy? They can afford to use and engineer situations that legally omit their normal taxation amounts substantially. So why should they cheat except for the excess greed or laziness aspect of setting things up by some. Many poor people cheat as otherwise they probably could not exist. There is just too much disparity between the top and bottom.

The average guy has far fewer things to participate in by the systems design. Or at least sensibly usable to him. Legal tax avoidance costs money and saves more for those in positions to take advantage of it. This situation is by no means exclusive to the United States.

Although I have a suspicion that out of self interest many bills have been passed to favour those with money in North America than other places. Too many politicians in North America are too well heeled financially to expect otherwise. Simply stated if the bulk of politicians where poor it is pretty obvious where the load would shift to.