One possible reason is that the PhD in some fields can be an "easy" way to get a paying position after graduating. There are a lot of smart people graduating fr

One possible reason is that the PhD in some fields can be an "easy" way to get a paying position after graduating. There are a lot of smart people graduating from undergraduate programs, and there is a general paucity of good jobs for these people. A PhD provides a few good things: 1) Credentials look good on paper 2) Work is generally perceived as interesting and worth doing (at least, until they start doing it) 3) Some fields/programs offer stipends. In many cases, a small stipend doing what you think will be interesting work is perceived as better than a larger salary doing an uninteresting task.