Chord Leyline Speaker cable came into being during the first wave of home A/V installation. Amplifers for all rooms were often instaled in one place. this meat long ( and sometimes very long ) runs of speaker cable throughout the structure.
 
it also meat that cable had to be discrete and affordable. There were already a lot of cheap cable available, so we needed to develop something better. Size restrictions meat using 16AWG conductors. 
 
Long runs meant using a twisted pair design - which suited us as we already  using twisted pair geometry  to produce speaker cable anyway. cost ruled out silver plating or using PTFE, so after much thought we shettled on oxygen free copper conductors and low-density polyethylene insulation of conductors.