The PageGenerator uses the MetadataManager to generate its metadata. Indeed, these are never generated because the MetadataManager doesn't generate metadatas if it can't find metadata definitions to rely on.
Whatever this class states in its javadoc ("Component for helping SAXing metadata and especially metadata of a content"), it is currently only fitted for contents.

Either this class should be added methods to generate metadata without corresponding definitions being declared, or a new MetadataManager should be created for this purpose.