If they were to use Twitter, Facebook, and Instagram for alerts, they’d hit 90% of the population.
Twitter used to be very reliable, that is no longer the case.
In this case they blocked access and that is the problem. Twitter decided, with no warning, to block all access without an account and logging in.
There is no guarantee this or worse will not happen again.
This broke the system in place. That is my point. Social media in private hands cannot be relied on to provide a time critical alerts like this.
The governments around the world screwed up by seeding this system to a private company that can be trusted to maintain a service. But they did it for the usual reason, it was cheap to implement.