I think the problem may more have been the lack of a sustainable revenue model. Getting volunteers to curate the directory is particularly destructive because the people who most want to volunteer either (1) want to promote something or (2) want to get paid so somebody else can promote something.
That's what search indexes are. Automatically curated directories.
It's just that the UI to the index is natural language queries instead of clicks through a graph, because the latter isn't scalable to large corpuses.
There are certain sites which have a landing page for every topic in some set of topics, you could add a lot of links quickly if you built rules for importing links from particular sites. Adding 10 sites a day with 1000 links each would be very possible, in 100 days you could build out a million links.
Google was caught flat footed and wound up buying and killing Freebase in order to catch up. They lied and said they rejected "semantic web" approaches despite hiring one of the leaders of the Cyc project as their head of research.
Still there is a difference between exposing that kind of database through a full text index vs exposing it through a browsing interface.