If you want to talk about the "history of music" you are basically talking about "biographies of composers" or, if you want to consider the 20th century, "biographies of musicians." If you want to pull in the most recent output of those who write and read music hisof tory, you could add the "ologization" of music history, where historical subjects are analyzed using non or quasi historical discourses (sociology and anthropology, for example.)
However, I would argue that if you go back to the "biographies of composers" era, another route of analysis exists, namely looking at the environment and human relationships of "famous musicians." This is quite easy to do using the techniques of social history, and it's a wonder that it is such a neglected era of inquiry- almost... not interesting to contemporary intellectuals. I honestly have no idea what Music Professors are doing these days, but they are not writing social histories of music. Also not writing social histories of music: history professors.
In fact, the only comprehensive Social History of Music that I have found is the one by Henry Raynor circa 1978. That is a generation ago. And it's not a popular book, either. I read A Social History of Music back in January and at the time I thought, "there has to be something more recent." BUT- I don't believe there is. And Raynor does a really, really good job of laying out the terrain is his introductory essay, which I am about to quote at length.
Raynor's approach has only one methodological flaw, and unfortunately, it's a whopper. Specifically he is a victim of "Bacon's Fallacy" which is the idea that the investgating intellectual must collect all the facts "as he finds them." I.E. there is a pretense of objectivity in the collection of factual information. Despite the flaw, the Introduction is a ready introduction to a Social Historian perspective on Music. Raynor notes that "music history" consists of two main themes: biographies of composers, story of music styles and their development. From this perspective (the non-Social Historian of Music) the purpose of Music History is to appraise specific Artists and approve their output as being significant. Raynor does not dismiss this approach as irrelevant, in fact, he thoughtfully observes:
"The mutability of stylicistic history does not invalidate what it has to say. A history of historians of music..would demonstrate quite clearly the function of historians as historians of taste."
Obbiously though, Social History takes a different approach in that is starts from the premise that music exists socially:
"It is written down so that people other than its composer can play it. The bulk of it presupposes the creative and interpreative efforts of two, three or up to a hundred performers. Most music presupposes the attention of the audience."
A neglected area of Music History is the attitude of notable Artists towards their Audience (What Mozart, Beethoven and Bach thought about the people who listened to their music) and the views of the Audience itself. A critical shift in this regard is the growth of the University in the 18th and 19th century, which led Artists, Audiences and Intellectuals to be much more detailed about their views regarding music. This shift reached it's apogee with the "neglected genius' Schopenauer, whose legendary contempt for the Audience was a watershed moment for Artist/Audience relationships- not to mention Intellectual ideas about that relationship.
As for an explanation for WHY the social history of music is neglected, Raynor has a clear villain:
"nineteenth century conceptions of art as pure activity, occupying only the higher strata as those which reckon up the bills and consider the possibility of paying them, that we do not consider the Artist's relationship to the musical world in which he must...secure performance and publication."I would say nothing has changed in that regard 30 years later- that quotation is still perfectly true when it comes to intellectuals and their ideas about music.