Talking about planned work repeatedly substitutes for actually producing it in Horkheimer’s later career.

Evidence

Just as he had once mentioned his book on dialectics at every opportunity, he now constantly spoke of continuing his philosophical work now that he had finished the Philosophical Fragments. But its continuation never progressed beyond the stage of notes. After Dialectic of Enlightenment, he only produced occasional works during the 1940s, and these would barely have met even his own standards for leading articles in the journal. — Rolf Wiggershaus, The Frankfurt School, 1683