Medieval Science, Technology and Medicine: An Encyclopedia

I am puzzled by the curious enthusiasm of publishers for expensive highly specialised encyclopedias. There are so many coming onto the market now, and quite a number of my academic colleagues seem to be involved with producing yet more of them. I cannot imagine that many individuals buy them. The primary market must be academic libraries and a small number of national and public reference libraries. I suppose that there are enough of us to justify publication, but the sales must be very small compared to the potential sales of, say, a handbook of medieval science, technology and medicine which...