This article is from the rec.music.reviews FAQ, by Al Crawford (firstname.lastname@example.org) with numerous contributions by others.
Probably because nobody has ever tried to post any. There's a hard core
of regular reviewers in the group, all of whom have distinctive tastes
and they review releases that interest them but might not interest you.
For some reason it's often the case that reviews of major releases
don't appear here. This isn't due to any sort of bias on the part of
the moderator, it's simply because no reviews of the album are ever
received. However, if no review appears for an album you're interested
in, and you go ahead and take the plunge by buying the album anyway,
why not review it for the benefit of less reckless souls?