Wall Street and the consulting firms developed business models that relied on the appearance of brainpower in order to win clients. This put a premium on recruiting from a handful of universities with the highest worldwide brand equity. Top students from Purdue or UCLA might be just as good, or even better, at putting together spreadsheets. But being able to boast that you have a team of kids from Harvard is important when you are trying to sell high-cost consulting and financial services of uncertain value.