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My grandmother is a university professor who has published her own textbooks and frequently contributes chapters to other textbooks and I've spoken to her about academic publishing very frequently.
In academic publishing, profit is not a consideration for the authors(this may be slightly different for the rare author who writes a seminal work in the field). Instead, publishing is done for prestige. For instance, for contributing a chapter to a book will typically only get you a copy. Publish your own textbook and you may earn about 300$.
It is the publishing houses who drive up prices, but greed still isn't the only factor here. The most i've paid for a book was $240 for my freshman organic chemistry class. It was a new edition and cost about 60$ more than the previous one, and the price set off a minor scandal in the class. Eventually one of the publishing reps can and talked to us. The price hikes were a result of some new highly technical pictures that the publishing house had to heavily invest in some specialized equipment to produce. Publishing is expensive. of course it also came out that the school was getting kickbacks from the publishing house, but thats a seperate issue.
Aside from textbooks, academic publishing is rapidly dying. If one were a history professor and wanted to publish a monogrpah, they would have an extremely difficult time trying to find a publisher. And the price of the book would be exorbitant. A regular sized book of about 400 pages might cost $200. It used to be tradition for the other professors in a department to buy a copy of a book one of their colleagues publishes, but this is no longer done because of prices. Indeed, it isn't even certain that the uni library will buy a copy of the book.
The same issue is with scholarly journals. For a journal that might put out 4 issues in a year, a library subscription might be 300-400 dollars.
The fact is that it is expensive to run a specialized press. You have to charge very high prices to recoup costs. Additionally publishing houses(even academic presses) are typically profit driven businesses.
The answer of course is electronic distribution. Academic publishing houses and university presses need to reevaluate their mission. The expense in formatting a tex document to distribute is miniscule compared to the price of running a press. Prices for the consumer should adjust accordingly.