But Matrix works fine if a hospital disconnects itself from the internet because of some DDoS or hacking attack. WhatsApp doesn't, because you can't host it on-prem. I am not sure about if governments have that use case, but we certainly have seen it in hospitals. (And even then, there are benefits of having patient data only on specific servers in specific environments, even if they are encrypted, because if you use WhatsApp to talk to your doctor, Meta will know about that. And I am pretty sure governments can appreciate such features as well.)