I think that Emil gave part of the answer. You can't get it, but want to learn is the other part. A third part is that several manufacturers have just simply quit making the chemicals used in photography and this includes sensitizing dyes and antifoggants. The demand for Hypo has gone way down and so has production while price goes up. What used to be shipped in tank cars now comes in 55 gallon drums.
So, laws prevent purchase, demand decreases and production either goes down or stops, but people still want to learn. OTOH, I must say that while early interest in workshops was world-wide, it is now decreasing to the US due to these problems and the cost of travel in some cases.
My book is selling well and I may have to go into a 3rd printing. And I've already had requests for V2.