Because parsing the original metadata from Project Gutenberg is time consuming to write. I wasn't going to submit it to HN until I had an index/search api, but someone beat me to it.
I was looking to write an alternative search for Gutenberg, based on the RDF dump, so would be happy to collaborate/discuss ideas.
I would love to have a complete python parser for the metadata. I strongly recommend collaborating with the Gutenberg package posted to HN a few weeks ago (and his rdf branch): https://github.com/c-w/Gutenberg/tree/migrate-to-rdf
GITenberg has a mailing list and would love to have you!