terminal – Some man pages missing from apropos / whatis database

I used apropos and whatis to look for some command, but didn’t find what I needed. But there is actually a command that does what I wanted (it’s sharing). It does have a man page (/usr/share/man/man8/sharing.8), and the man sharing command displays it as expected.

However, this command and presumably many others don’t appear in any of the 2 whatis databases that I seem to have. The files I have are /usr/share/man/whatis and /usr/local/share/man/whatis. The whatis and apropos commands seem to search both.

So I tried to refresh them by running sudo /usr/libexec/makewhatis. It did update the /usr/share/man/whatis file, but this particular man page (and others I guess) is still missing.

I tried this on 2 different machines. One running High Sierra, and the other running Mojave.

Why are some man pages not listed, and is there anything I can do to have a reliable whatis database?