The Signal messenger and protocol.

It's 100% logical for a country to keep critical infrastructure, which secure messaging is, domestically independent from external influences.

Not to mention signal is centralized in the US, stores the master key in the cloud... Both of which are no goes if you're trying to maintain independent critical infrastructure.

The French government uses email, which is federated, and can be run independently.

So the real issue is the signal CEO is not moving towards protocol independent federation where the French government could maintain their own infrastructure, and talk to the signal foundations infrastructure. Saying my walled garden is a nice walled garden, they really should be in my walled garden, isn't really going to change the security threat model considerations at play here.