Why does musl ldconfig ignore standard directories?

I was trying to make a docker container based on Alpine linux. During installation of some software I noticed that shared libraries were not installed properly. After some investigation I found the musl ldconfig to be ignoring standard library directories.

The ldconfig script contains the following:

case "$FILE" in
    /lib/*|/usr/lib/*|/usr/local/lib/*) ;;
    *) [ -h "$LINK" -o ! -e "$LINK" ] && ln -sf "$TARGET" "$LINK"
esac

What is the reason for this?