They died because the web is so large that it's somewhere between cost-prohibitive and impossible to index directory-style manually (which is how directories us

They died because the web is so large that it's somewhere between cost-prohibitive and impossible to index directory-style manually (which is how directories used to be maintained). And nobody's come up with a way to automate it that's been effective and not subject to gaming by spammers. Additionally, categorization is useful for quickly answering only a tiny subset of query types.