The reason is not known, but back in the fourteenth century a list or roll of names was called a ragman.
Later this was altered to ragman, and the list itself was generally called ragman roll.
Perhaps because, like in a dictionary, the subject matter in a list or roll changes frequently, ragman roll became equivalent to a series of disconnected statements.
In the process its own name became altered, by the eighteenth century, to rigmarole.
