Government entities generally follow the principle of “We go where the people go”. If the majority of people are using Twitter and YouTube and Facebook, then that’s where the government bodies will host their accounts. You’d need a way to ensure that their message will reach their audience before you can even begin getting them onboard with the process of creating and setting up a whole new social platform. And that’s going to be the hardest part to sell, since Mastodon is still among the least-used platforms available. Either show up with the critical mass needed to ensure that they’ve got an established user base, or show a plan to reach that point.
Because when you see somebody with -1000 karma, it’s a pretty good indicator that you shouldn’t waste your time engaging with them.