On early Unix systems, the directory structure was a simple 16-byte record; 14 bytes for the name, and 2 bytes for the inode. [1] strncpy() was used to simply record the file name into this structure.
[1] "UNIX Implementation" by Ken Thompson, _The Bell System Technical Journal_, July-August 1978, Vol 57, No 6, Part 2, pg 1942.
(I don't use strncpy and don't defend its functionality, just want to know what was intended when it was introduced.)