The high prices could be due to just the opposite problem: professors are particularly difficult to sell to. They are individually picky about how their subject matter is presented, and textbook meetings (where we try to agree on the textbook among colleagues at a particular school) are frustrating and difficult.
The time and effort expended in selling those books are (probably) enormous. There's no institutional path-to-sale. Decisions are made by the professors themselves, meaning it's close to b2c marketing of a b2b product. The problem, in business terms (stolen from a VC spiel to an entrepreneur group as to why they don't fund educational software) is that "the customer is dysfunctional."