Summary: CR+LF was in common use because it directly descended from commands used to directly manipulate a printing head. Multics started using LF only because

Summary: CR+LF was in common use because it directly descended from commands used to directly manipulate a printing head. Multics started using LF only because by that time the hardware was abstracted from the software, and Unix later followed this convention. See also, https://en.wikipedia.org/wiki/Carriage_return https://en.wikipedia.org/wiki/Carriage_return, which describes more about how early CR was used.