In response to Joe Biden and the White House enabling ActivityPub federation via Threads, a number of people asked: "Why didn't the White House just self-host their own Mastodon server?"
Here's some very basic musings on what it would take for that to happen. and what some of the hurdles are. Don't consider it a definitive answer, but a jumping-off point.
One thing that people seem to take for granted is that these government-hosted instances would be open to the public for account creation, while this doesn't necessarily have to be the case. Not everyone can get a statedepartment.gov email address. Not everyone needs to be able to get a @statedepartment.mastodon.gov handle. Just leave it to public officials only.