If DIR/public does not exist, ezmlm-manage(1) and ezmlm-get(1) modify their behavior. They disallow user requests, but for remote administration lists, honor moderator requests. Thus, for a remote admin list without DIR/public, only subscription moderators or remote administrators can receive archive retrievals and only remote administrators can subscribe and unsubscribe user addresses.
If you'd like this restriction of archive retrieval with maintained user-initiated ezmlm-manage(1) subscription functions, use the ezmlm-get(1) -P (not public) switch, and retain DIR/public. Also, look at the ezmlm-make -b switch.