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, which describes more about how early CR was used.

> ... functions concealed the fact that the print head could not return from the far right to the beginning of the next line in one-character time.

Oh, cool, I didn't know that bit. Interesting!