David Damrosch has a thoroughly accessible essay in the Chronicle of Higher Education about the difficulties scholars face when they try to write for a wider audience. This paragraph in particlar explains why academics generally don't do this all too well:

The problem isn't that academics "can't write," as is often claimed, but that we are typically engaged in what scholars of the Renaissance know as coterie writing. In 16th-century England, for instance, small groups of aristocrats such as Sir Philip Sydney, his sister Mary Herbert, and their circle would compose poems for their mutual entertainment, circulating them privately from one country estate to another. Scholars today may reach a somewhat larger circle, but most academic writing is part of a continuing conversation among a coterie of fellow specialists with common interests and a shared history of debate. Even for scholars who are elegant prose stylists, it isn't an easy matter to make the transition from writing for Milton's "fit audience, though few" to a larger but less fit readership.

Not only did the people at Holt want the book I wanted to write — antiquity and all — but they also suggested ways I could revise my sample chapters to better effect. The "Aha!" moment came when John Sterling, Holt's publisher, pointed to the opening of my first chapter. I had begun with a flourish, emphasizing the excitement created when a young curator at the British Museum first deciphered the Gilgamesh epic, with its seeming confirmation of the biblical story of the Flood: "When George Smith discovered the Flood story in the Epic of Gilgamesh in the fall of 1872, he made one of the most dramatic discoveries in the history of archaeology." Sterling ran his pen along these lines, but instead of praising this bold beginning, he tapped the page and asked, "Couldn't you make this opening just a bit more dramatic?"

He was right. I had told the reader that George Smith had made a dramatic discovery, but I had failed to dramatize the scene at all. Rewriting my opening, I placed Smith at the long trestle tables where he worked amid the watery sunlight coming in through the museum's windows. I went on to detail his awkward social position: Never having gone even to high school, he had been apprenticed as a bank-note engraver. Brilliant and ambitious, he had taught himself Akkadian and begun to haunt the museum's Near Eastern collections during his lunch hours, making his way up from Fleet Street through the press of carriages, pedestrians, and hand-drawn carts full of cabbages and potatoes.

With the scene now set, Smith was on his way, and so was my book. I could still make my central cultural and political points, but they had to be carried by a strong narrative line, built around intriguing characters and fleshed out with a judicious use of telling detail. An ominous mongoose, for instance, made an effective lead-in to a chapter on the Assyrian empire, "After Asurbanipal, the Deluge." The mongoose's sudden appearance beneath King Esarhaddon's chariot led to a revealing exchange of anxious correspondence between the king and his chief scribe, who tried to reassure the king that the mongoose was not a warning sign from heaven but merely a bit of imperial roadkill.

The lesson I would draw from my Goldilocks experience is that it is neither necessary nor desirable to dumb our projects down when writing for a general audience. At the same time, we need to write quite differently when we want to reach beyond the comforting confines of our disciplinary coteries. It is good to have a clear and vivid style, but equally, we have to retrain ourselves to write for readers who don't already know what we're talking about, and who need to be shown why they should care about the things we know and love so well. The trade market can bear an impressive degree of scholarly substance if we can teach ourselves to reach out to a substantial nonscholarly clientele.