They are _used_ very extensively, but not in web pages. Many industry domains rely heavily on linked data and ontologies. It's true that they are less commonly

They are _used_ very extensively, but not in web pages. Many industry domains rely heavily on linked data and ontologies. It's true that they are less commonly embedded as semantic data in web pages. There's a real bootstrapping problem there: no reason to embed data if no tools will read it, no reason to build tools if there's no data to read.