<p>I think so few people do it because it makes there is very little return for the cost. Tuition at a private university is extremely expensive. Have two undergrad degrees is basically worthless (as opposed to just double concentrating). If you are interested in learning about a science and a subject in the humanities, Brown is a perfect place to combine those interests and engage in them in detail. But why would you pay extra for a second (equivalent) piece of paper. Most people just go to grad school and get an advanced degree (masters) for the same price.</p>