In practice, as I understand it, `so` doesn't achieve anything
for man
pages that can't be done with symbolic links and (importantly) a
man
page indexer that is symlink-aware. Perhaps `so` support was
preserved,
and its practice retained, for a long time because at one point
in the
1980s I think there was an AT&T/BSD split over symbolic links
even being
supported by the kernel. (And, to be fair, symbolic links are
something
of a hack that can make file system operations more painful. I
see from
the nftw() man page that they were still doing so as late as
glibc 2.30,
3 years ago.)
Does this help?