These are the backing blocks for the dies. There is no reason to make them from hardened steel as there is little pressure on them when you are only bending 3/4 tubing. Besides, they are heavy and hard to deal with when they are made out of solid steel. If I were going to bend a million tubes, I'd make them out of hard steel.
Incidentally, this is what they call "hard" and "soft" tooling. Soft tooling is easier to make and costs less, but doesn't last as long. "Hard" and "soft" is an industry standard term.
