Maybe but I think it is more like how most people don't use SMS for messaging vs some kind of internet based app/ecosystem. SMS/telcos couldn't support what people needed, multimedia support, group chats etc. I think the use of Twitter and social media in general would be similar for these government groups. They just have better tools.

I think the best approach is to still use Twitter but also use all Social Media like Facebook (especially), Insta (hard to do for text) but you could link to their Website with the same posts/info.

In the end you have to try and inform the public where they are, just like would happen on TV or Radio in the past.

Maybe it is actually a space for Google/Apple/Microsoft/Linux as OS makers to provide some functionality to do this kind of broadcasting over the internet in addition to working with Telcos for SMS/mobile based alerting.