The great Jerry Byrd had to take a job painting houses in the 1960's when his sessions and gigs fell off. In later years he said that he had made no money on his many albums. He also lambasted someone on line for copying and selling his steel courses. He said he needed that income in his retirement. John Hughey also blasted someone on line for uploading and sharing his latest album. I don't blame him for that, but it was clear that he depended on that income.
Buddy made a couple of surprising comments late in his career. He said that playing occasional steel shows and selling his courses gave him "Walmart money". And one time here on the forum he said that recording studios would occasionally "throw me a bone". Not sure if he was joking, but it was a surprising comment.
I agree that a lot of great steel guitarists were just sidemen, especially under the old Nashville "Star system" The players were just hired hands, just wallpaper behind the Star.
On the bright side, some steel guitarists who expanded into music sales and teaching, like Jeff Newman and Eddie Alkire, did pretty well. And some who fronted bands... Alvino Rey, Robert Randolph, Santo Farina... must have made a good living.