Monocultures reinforce bad habits. I have friends at a wide variety of tech companies - Microsoft, Google, Facebook, Amazon, Tableau, AirBnB, and more. All of us know, in broad terms, what the others do. We don't discuss trade secrets or specific unannounced projects, but we're able to talk about things like "X works on Storage Spaces for Windows, Y works on WebXR, Z works on security, etc."

We're also all able to talk freely about what aspects of our jobs and employers we like and don't like. This is valuable information - for instance, I've heard enough first person anecdotes from various teams to know that I'm not interested in working for Amazon unless all other avenues to pay my mortgage have failed.

The Apple experience sounds like my interview with the NSA years ago. All of my attempts to ask any questions were met with a "no comment" for the most part. Very frustrating experience. I walked away with not much more idea of what a job there would be like than you could get from reading Wikipedia.