The reason being that with tika bridges, the users only implement TikaMetadataProcessor, not the FieldBridge.
Thus they cannot implement MetadataProvidingFieldBridge. Adding fields with a different name from the one passed as a parameter becomes difficult (with Lucene, because the field can't be made sortable) or impossible (with Elasticsearch, which expects metadata for every field).
Note: there are tests that should pass when this ticket is resolved, and that are currently disabled in the pom.xml of the Elasticsearch module. Those tests will be (or have been) outlined as part of HSEARCH-2390.