I think being smart is more of a state of a person than a property of a person, kind of like health. Genetics plays a role in it (you can be born unhealthy) but so does the environment. I think extreme success in the modern world creates a very unhealthy environment for the state of your smartness.

After all, if I am to believe what Mercier and Sperber are saying in "The Enigma of Reason", reasoning evolved not as a tool to find the truth and make good decisions but as a social tool - to convince others to cooperate with you, to justify your actions in front of the others, to secure your social status. If your cultish following showers you with cheers no matter what you say or do (especially if you label your critics by that label that your followers hate - woke, ideological, racist, censors, or whatever), how can you not lose contact with reality?

That is the simplified version of my explanation for the phenomenon of previously really successful people saying and doing borderline insane stuff. I could name 10 famous people in the last 3 years that IMO fit that pattern.