8. There are very few jobs.

After the massive post-war expansion of American higher education, academic departments became increasingly dependent on graduate-student labor in order to maintain a research focus while educating undergraduates. Universities require every faculty member to produce a steady stream of publishable scholarship (see Reason 33), meaning that the time professors have to devote to teaching is limited. To meet their teaching obligations, universities need a steady stream of graduate students in all of their departments to serve as teaching assistants. Some graduate students actually graduate (see Reason 46). As a result, there is a steady stream of newly minted PhDs walking, diploma-in-hand, out of every department of every research university in the United States.

Having spent as many as ten years (or more) studying, teaching, and researching as graduate students, most new PhDs want to put their skills and knowledge to use in the university setting that they know so well. They are often in their thirties when, for the first time in their lives, they are finally qualified to earn a regular salary in their chosen profession. But there are only so many regular faculty positions to be filled. Open positions are usually the result of retirements, but there are never as many retirements as there are new PhDs (see Reason 55). This means, of course, that more and more people are constantly competing for fewer and fewer academic jobs. The problem has been compounding for decades. This is why some Ivy-League PhDs find themselves working at community colleges (see Reason 91), and why many PhDs find themselves in temporary teaching positions (see Reason 14), often earning less than they once made as lowly teaching assistants.