In WorldCat Discovery, filters vary by database based on the metadata available. This means use of the Audience filter is based on the databases included in a search, including searches done via Advanced Search. While Audience is included in metadata for WorldCat and WorldCat.org, it is not available in all central index databases. WorldCat Discovery displays filters that work best across all databases being searched simultaneously.
For more information see Filter and refine search results and Search Settings.