To comedians, “material”—their jokes and stories—has always been precious, worthy of protecting and preserving.
Compare and contrast the materials of comedians versus magicians.
Collection was an important piece. Protection/secrecy was relatively similar, though with a joke, the item was as ephemeral as a magic act which would have been confounding on it's nature.
Link to Ricky Jay's collection of magic acts and pieces. Other comedy collections include George Carlin, Joan Rivers, etc.