Yeah - it is just a simple matter of numbers as opposed to pretentiouses or humblebragging. The number of people interested in a book is highest for the surface/casual level and it is seldom that there will be enough demand for often expensive and slow to move texts. There isn't much call for say republishing of authenic 19th century surgical technique books. Maybe some casual readers would buy it at a lower price point but almost certainly not if it is several hundred dollars.