Even if the technical info is not under seal, the details of how Pegasus used WhatsApp servers might give away enough info about the WhatsApp servers to either open them up to another attack - or open them up to a legal challenge from one or more users over not taking due care and so exposing their data. IANAL, can't weigh in on the latter, but if they've been using obscurity in place of security, disclosure would really be inviting another attack.