It's something aimed at popular (meaning general, or non-professional) audiences, rather than other historians.

If a historian publishes an academic history (meant primarily for other professionals in the history profession), it's expected that he or she will spend some time reviewing where the work fits in with the historiography of the subject, will write about the theories and historical traditions that informed the research, and might make reference to jargon or names that other professionals will easily recognize.

This kind of thing is usually a turn-off to general readers, who aren't sufficiently knowledgeable about any of these things to make use of this kind of information. So writers producing popular histories typically leave this kind of background out, and focus on producing a narrative (with or without an organizing thesis) that has a clear storyline that will appeal to a general audience.