it helps to be smart and have credentials, which all those authors are/have

Definitely they're smart, but most of them just started writing and built up a following that way, and that became its own kind of credential.

Jeff Kaufman started writing in his freshman year of college (https://www.jefftk.com/p/webpage-up), Matt Y also started as a college student (https://www.washingtonpost.com/lifestyle/2023/01/11/matt-ygl...). Dan Luu's linkedin tagline is just '???'.