What was the primary factor encouraging mainstream economists to marginalize post Keynesian theory?

Paul Samuelson’s own words are used to demonstrate that he and his “Keynesian” followers never comprehended Keynes’s general theory or the Post Keynesian development of Keynes’s analysis. Samuelson claimed that Keynes’s theory is a slow adjusting Walrasian system and any theory which rejected the Walrasian foundations is not a valid economic theory. Samuelson’s arrogance in believing he had discovered the “Foundations of Economic Analysis” is the primary factor that has marginalized Post Keynesian theory. Keynes had explicitly rejected Walras’s system. Sidney Weintraub, a founder of Post Keynesian theory, developed the Marshallian micro foundations that are the foundations of Keynes’s general theory.