Disambiguation pages should not be listed in [[Special:Lonelypages]] because
there's a conflict of interest: disambiguations should be solved and they don't
necessarily need to be linked to, so they could be "lonely" (that's what
[[Special:Disambiguations]] is trying to achieve). Since there is already a
trigger for a page to be listed as a disambig (the template), I think it's
fairly easy to exclude those pages from the list of lonely pages.
See Also: T8651