The main obstacle to making such a thing isn't Amazon. It's that there isn't a big enough market for large e-ink displays to create a mass market for them. As a result, the displays are very expensive, and the result is that such an e-reader is too expensive to be popular.
Another problem is the lack of color. Many current textbooks use a lot of it.
Finally, there is the competition from tablets. If a large e-reader costs as much as a Microsoft Surface, most people will buy the Surface instead because it does more. People can justify an additional $100 device like a Kindle Paperwhite, but fewer can justify an additional $500 or $1000 device.
My guess is that a large e-reader would have to sell for $250 or less to have a chance of widespread success. Currently it is impossible to hit that price point because the display costs too much. And until a large e-reader or some other product creates significant demand for large e-ink screens, the display will always cost too much.