When had all sms or phone service in your country gone down? Sure a carrier might have issues - but there are other carriers who can pick up the load and there are likely government contingency plans for just that situation.
The sms and phone service infrastructure is more centralised than you might think and carriers probably have less redundancy than big tech when it comes to it.
What I’m talking about here isn’t my WA group chat with my soccer team.
I’m talking about 911 being reachable, or about government communication with its citizens etc.
For these bigger use cases, there are contingency plans. For example, 911 will remain reachable via other carriers for you even when your carrier goes down.
For some governments, WA is in the critical path for these use cases. And you can’t route around WA as it’s one product by one company who is the sole maintainer of it.
Same doesn’t apply to WA.