Probably because to most, it doesn't matter. Either from viewers who are just interested in the artistic side of it or from the artists themselves who don't believe the technical details are all that important. Plus, such detailed technical specs could clutter the layout of a photobook and detract from the central element of it - the actual photos. There may also be those who believe their process is 'theirs' and thus they feel the need to keep it to themselves. There are examples of this in pop culture, look at Breaking Bad for example. Egos can very easily get in the way of things.