I don't know. We'd have to ask them, and they're dead, so we'll never know, but it's not a silly question at all.
My experience w/ this is that creative types of that caliber mainly focus on themselves and their work, and they don't have the time. It's how they got to be successful. It's not smart to give away your hard earned secrets either.
When I lived in Las Cruces, NM, there was a small town just outside of it called Mesilla. It was an old farm community that was trying to make itself artsy. They had a wonderful place that was a combination B&W fine art, digital photography gallery/workshop space. One day I was talking to one of the gallery sales people and asked them if they liked working there. They replied that it was fine, and a whole lot better than dealing with painters every day. Being a painter myself (and occasional photographer) I asked them what was wrong w/ the painters. She said....."Look, they would walk into that gallery and the Mona Lisa could be hanging on the wall, they didn't care. They would not even see it, just go right up to their painting, go get me, and snarl 'Why is MY piece hanging in this crummy location!"
You need that sort of one point focus to get anywhere in the arts. There's a LOT of competition and only so much wall space. The people that you mentioned probably had that sort of mind set. Ansel Adams did make some good instructional videos toward the end of his life, and others were mentors to other photographers, but that's different.