Why? Well, what is it that we use to train AI? Human generated content. What is the most revolutionary AI technique that came out recently? Direct human feedback during the training process. Do you see a pattern here? If we attempt to feed AI generated content to train other AIs all performance metrics drop... Its a chicken and egg situation if a human mind is the best content creation device we have, how anything trained on that content can surpass it quality wise?
Of course AI having very fast access memory compared to our meatware can recall more and faster, but this is _just_ a quantitative improvement. Not a qualititative one.