You hit the nail on the head. It sounds silly to say, but it simply is useful to know things. And to know things, you "memorize" them. More specifically, you build neural pathways as the information becomes better known to you, and which can be activated quickly. This is why I maintain a massive Anki deck for anything I find curious and want to remember, inspired by Michael Nielsen (https://augmentingcognition.com/ltm.html) and others.

Even if AI is very powerful, it is very obvious that someone actually knowledgable in a given domain can leverage AI more usefully than someone without that base of knowledge. And to be actually knowledgeable, as opposed to vaguely familiar with terms, takes significant effort over time. Luckily we have tools like spaced repetition that make that effort easier.

The last thing I'd add is that it's useful to know lots of things in various domains. Much like an LLM, our brains draw connections between disparate things which we know well, in the process of diffuse mode thinking.