I think he is by default less interested in gigantic black box systems that he can't fit in his head, and that secondly he has read Gary Marcus thinkpiece and was persuaded by him, and thirdly I feel like there might be some kind of religion thing but I don't have direct evidence of that third one.
Here is what Knuth has said, related to why he isn't as curious as you might expect:
> "Gary Marcus's column in the April CACM brilliantly describes the terrifying consequences of these developments. [...] I myself shall certainly continue to leave such research to others, and to devote my time to developing concepts that are authentic and trustworthy. And I hope you do the same. [...] The topic [LLMs] is timely, and important enough not to ignore completely, but it's emphatically not for me."