Not as prolific as these winners, but
Daniel Keyes - Flowers for Algernon
William M. Miller - A Canticle for Leibowitz
William WalterM. Miller - A Canticle for Leibowitz
Keyes - what sf did he write besides "Flowers for Algernon?" One short-story - later expanded into a novella - is simply too little for the author to be included in such a list.
Miller? His short-story "A Canticle for Leibowitz" was a masterpiece - light-hearted, intelligent, and imaginative. But the three-part book he developed out of it is unbearably pessimistic and depressing. Wasn't surprised that he committed suicide.
Regards,