That would explain it. But then again, why not use Signal or something similar for sensitive topics.
https://www.wsj.com/articles/wall-street-to-pay-1-8-billion-...
Article is paywalled, but how can it be proved they’re using something like Signal? There must be at least some discussion available to be disclosured on request by law? How do they define if the subject is relevant enough to require a formal exchange between executives?
The world of big public companies is fascinating.
The threat model for signal is not to get you out of your legal obligation to comply with court orders.