There is a very nice chapter in the somewhat dated but classic book Business Adventures [1] on trade-secrets and what happens when employees of one company move to another. In chapter 11, "A man, his knowledge, and his job", there is a story of a "space-suit" manufacturer Goodrich suing an employee for moving to its rival Latex for stealing trade-secrets. The story is timely in context of Meta hiring researchers from open-ai, deepmind etc for 100s of millions for the knowledge in their heads of the recipes which work for making superior LLMs - the knowledge of which is empirical and may take years to discover.
You could also argue that they're hiring people for the general expertise they have in developing frontier LLMs. Distinguishing trade secrets from general knowledge is difficult and employees building the latter to make them more valuable to new employers is an explicit policy goal of US employment law.
FWIW, outside of the chapter bwfan123 references, this entire book is an excellent read. Great stories and even better writing - it's one of my personal faves :)
[1] https://www.amazon.com/Business-Adventures-Twelve-Classic-St...