That's pretty much entirely in the hands of the universities and professors. To a large degree this is really a US-specific problem, US textbooks are easily 2-3

That's pretty much entirely in the hands of the universities and professors. To a large degree this is really a US-specific problem, US textbooks are easily 2-3 times as expensive as elsewhere. And the cause is likely that US universities require specific textbooks for courses, which is not how it works e.g. in Germany where I studied. I had a single course that required a specific textbook, which cost like ~50 EUR at regular price. Every other textbook I bought I selected myself, and they almost all were really worth their price. Requiring specific textbooks in specific editions removes all market forces and direct competition. It also kills the second-hand market and makes it much more difficult for libraries. When students are free to choose which textbooks to buy or rent from a library you get a much healthier market.