I presume you know Zelenka as well, a contemporary of Bach's (both knew each other and respected each other as composers).

There were a lot of these components in middle Germany at that time. Basically every reigning dynasty employed one, and there were a lot of those. They aren't famous now, but Bach wasn't famous at that time either. That he is famous now, is due to Mendelsohn.

Jan Dismas Zelenka wrote for the Saxon king, and many of his works were never released as a result.

Then, they burnt to ashes in 1945. The only extant copies were caught in the bombing of Dresden. We tend to think of "lost works" as something that happened in Antiquity. Nope.