Google Closure Compiler doesn't get any use because Google has entirely neglected it for a decade. They could have been where TypeScript is today, but instead they entirely ignored external users, hardly staffed the project, and now have an inconsistent mess with a non-coherent super-buggy type system and no users. It's a disaster, and if you try to do anything non-trivial it will fall to dust.
Good riddance to that abandoned pile of rubbish, and fuck Google management for letting it get so bad. They had a five-year lead on the rest of the industry in serious JavaScript development, and now they're ten years behind.