Intelligence, like physical ability, is trainable within limits; the general belief appears to be that such limits are genetically determined and vary widely among human beings, but it also seems clear that the vast majority of human beings never even approach those limits, for the same reasons that most people don't become Olympic-level atheletes, even if they have the genes for it - they don't put in the time training and improving their abilities, or they're hobbled by injuries of various kinds.

Now if you have an objective goal such as improving mind-body performance across many different metrics, LLMs can be an aid - you can have them help with designing and developing physical and mental training regimens on a daily schedule, pointing out flaws in your understanding, etc. As for the article's thesis, you could spending 15 minutes writing a prompt about whatever author strikes your fancy and then have the LLM dissect, critique and grade your effort if you like, then rinse and repeat - just as with lifting weights, your short essay skills will improve.

As to why many people don't seem interested in following such rigorous programs, we could blame consumer capitalism, advertising aimed at immediate gratification and the promotion of addictive behaviors for short-term profit, on one hand, and fear among the ruling classes of an educated informed and indepentenly-minded population, with a resulting emphasis on rote memorization and appeal to authority over critical analytical and creative skills, etc., on the other.