A list that tells you where things are rather than holding them. A directory is a map of a place, kept in the place.
Latin directorium, a guide or set of rules, from dirigere (to guide); later specialised to a listing of where things are kept.
Its root once named a guide or a set of rules to live by, not a simple listing; the word narrowed only later to the plain map it is now. A directory still keeps that older trust, it is consulted, not merely read.