Chamber sleeving originally was a method used to convert paper case chambers to accept thin brass hulls. See J H Walsh "The Shotgun" for explanation and description of methods used.
I suppose a few gun owners may have resorted to chamber sleeving in order to use thin brass hulls. But I seriously doubt if that was a common reason for it.
I've pretty much always seen rusting, pitting, or other chamber damage as the primary reason for chamber sleeving, especially when the damage created extraction problems.
