Why do they train specialists for generalist work?

The task of writing a PhD dissertation is almost completely opposite of what university lecturers do in the class room. In graduate school you write a detailed work on a limited subject. My own dissertation was a comparative study of about a half century of modern history of three national groups with a total combined population of less than three million people. As a lecturer you teach the broad history of whole continents for periods of time stretching for centuries. Writing a dissertation on the comparative experiences of internal exile in Kazakhstan, Central Asia, and Siberia of Russian Germans, Crimean Tatars, and Meskhetian Turks is probably not the best possible preparation for teaching nineteenth century European history.  I think Soviet, Russian, or maybe even Ottoman history might actually have a more direct relationship with the subject of my PhD dissertation. Had I known I was going to be teaching European history despite the topic of my dissertation and publishing record I would have spent more time in Arivaca reading about England, France, and Belgium. Back then I thought I would be teaching the history of the Islamic world.  It turns out that the specialist approach favored in academia for dissertations and publications has almost no application in the classroom. There the more general, particularly regarding breadth of time and space, the better. A working knowledge of all the important events of world history from Middle Ages on is more useful in university teaching than specialization in anything.