The market is too small to make some of these items commercially and some of the items you want are at the edge of what people can or will make at home.
So, you can make an Azo type paper in 3 grades and a Kodabromide paper in 2 grades. You can make an ISO 1 - 40 emulsion that is blue or ortho sensitized. Beyond that, things start to get difficult and expensive. They can also get to be very time consuming.
So, we, the teachers and writers of this stuff try to formulate things that are very useful but take a minimum of effort and expense. Of course, it sometimes takes thousands of dollars of R&D to make these work. Most writers freely admit that they have not make the emulsions that they publish. They just copied it from somewhere. And, almost all of those in books are wrong due to omission or comission. Grant Haist published a formula in V2 of his book set and told me that it was heavily edited by the Kodak editors.