I don't know what the reason was, but you can probably find someone mentioning it by searching the threads referencing the publisher in comp.lang.lisp, from 5-6 years ago.
http://oreilly.com/oreilly/author/writeforus_1101.html
"Books on topics that have dismal sales despite quality books being available. (If you're addressing a topic where good books have sold dismally in the past (for instance, LISP, LaTeX, or Web-based training),"