>> Why is management consulting a billion dollar industry?
Because most rich people are idiots but they have direct access to money printers via hundreds of legal money laundering schemes going on in the background so they can afford to waste as much of it as they want on whatever they want and still be profitable.
Why is management consulting a billion dollar industry? Are there that many clueless executives running F500 companies (pretty much all of them).
Or perhaps your understanding of management consulting isn't quite right.