Having worked for an Academic Publisher that had intense interest in this I finally came to the following conclusions to why this is DOA.

1. Producers of content are unwilling to pay for it (and neither are consumers BTW) 2. It is impossible to predict how the ontology will change over time so going back and reclassifying documents to make them useful is expensive. 3. Most pieces of info have a shelf life so it is not worth the expense of doing it. 4. Search is good enough and much easier. 5. Much of what is published is incorrect or partial so.

In the end I decided this is akin to discussing why everybody should use Lisp to program but the world has a differ opinion.