That or they were very good at faking it.
People will find ways to get the time and rest they need, hiding and faking is less effective.
On top of that you get loyalty in return for being treated as human beings rather than slaves.
Of course companies that do that are usually startups, and if your startup tries to fuck you, leave. They probably need you more than you need them.
The culture aspect needs to come down from the top. A senior engineering manager at a well-known SV company with "unlimited" vacation claims it works pretty well because, from his perspective, an expectation that you'll take time off and disconnect comes from the top. On the other hand, I've heard others at the same company give a less rosy report, so YMMV depending on teams, etc.