Part of it is, indeed, talking about unspoken rules. But part of it is that the hiring managers and CEOs are humans like everyone else - some may have ego issues, or buy a little too much into their company's branding.

Exactly this. The first rule of fight club is don't talk about fight club.

What surprises me more: Many people don't think interviewing is a game. They think it is straightforward and "rules-based". I guess those same people also believe PR. :)

Or want the world to be fair and honest, and - per the well-known saying - they are themselves the change they want to see.