This is pretty obvious, but I don’t think I’ve seen it so clearly stated:
Academic historians now write almost exclusively for one another and focus on the issues and debates within the discipline. Their limited readership —many history monographs sell fewer than a thousand copies— is not due principally to poor writing, as is usually thought; it is due instead to the kinds of specialized problems these monographs are trying to solve. Since, like papers in physics or chemistry, these books focus on narrow subjects and build upon one another, their writers usually presume that readers will have read the earlier books on the same subject; that is, they will possess some prior specialized knowledge that will enable them to participate in the conversations and debates that historians have among themselves. This is why most historical monographs are often difficult for general readers to read; new or innocent readers often have to educate themselves in the historiography of the subject before they can begin to make sense of many of these monographs.
The problem at present is that the monographs have become so numerous and so refined and so specialized that most academic historians have tended to throw up their hands at the possibility of synthesizing all these studies, of bringing them together in comprehensive narratives. Thus the academics have generally left narrative history-writing to the nonacademic historians and independent scholars who unfortunately often write without much concern for or much knowledge of the extensive monographic literature that exists.
(Gordon S. Wood “The Real Washington at Last” NYRB 9 Dec 2010)