Mastodon is irrelevant for government purposes for that reason. They would do it if it had a large number of people.
Governments and corps are in the same battle for eyeballs as everyone else. They can't win that by being away from the eyeballs.
Government could limit updates to a town crier. But the end result of that is far fewer people get the update, not that everyone goes to see the crier.
The EU has an instance at social.network.europa.eu
There's a Dutch one at social.overheid.nl
There's a Swiss one at social.admin.ch
There's a German one at social.bund.de
I'd be pretty happy to see some kind of law mandating that they have to host their own content, and publish news / alerts via RSS or some equivalent - and if social media / big tech want to scrape and republish that, fine, but they shouldn't get privileged access to it.
If nothing else, they should have a "press pool" equivalent, where content goes to several providers at once and never exclusively to one platform.