I have worked with C-level executives at several very large companies. Due to the nature of regulation at companies of this size, many of these individuals are under subpoena almost continuously. As a result of the record keeping requirements of a person under subpoena, their life is much simpler if they conduct all business in person and keep no files. They use e-mail exclusively for interactions that are intended to be public. Any business communication to them is usually scheduled through a secretary and done in in-person meetings with projected slides.
It's not that they have anything to hide -- but at the same time, corporate espionage is a real thing and you have to protect trade secrets and you know the government receives a copy of every e-mail and document that you do.
For interest, at a previous company were told to cc in legal for sensitive communications and write something in the subject header to say it was confidential and for legal review, even though you had no expectation for them to join the conversation. This put the emails into some privileged information category. It wouldn't stop a court getting access if they wanted to read comms but it significantly increased the benchmark to gain access as it was a client lawyer conversation.
Not necessarily. They just don't want the risk of their emails being used against them due to misinterpretation.
A great story I heard from a former employer was a lawsuit around a new sleeping pill. One person taking the drug ended up killing his wife while on it (in combination with a ton of alcohol and other drugs). The drug manufacturer was sued and decided to vigorously defend the safety of the drug.
Well, some low-level lawyer in the company decided to spout about the science of drug development (have no actual education around it) and said in an email "maybe the dose is too high?".
Slam dunk. That statement looked incriminating. The company quickly settled after that email was found. Just not worth the time or money to fight it. A settlement was the cheapest way out.
The phrase "something to hide" has a loaded connotation that implies wrong-doing. Everyone has something they'd rather not be public, but the phrase means more than that.
To add to this, there are also lots of things that can be misinterpreted or taken out of context. I imagine that most people would treat email differently if they knew that all of their emails would become public information. Smart executives at large companies simply assume this and send emails accordingly.
It's not that they have anything to hide -- but at the same time, corporate espionage is a real thing and you have to protect trade secrets and you know the government receives a copy of every e-mail and document that you do.