It's not, though it does get partial funding from the US government. I've been for a few weeks now to try and unpack the ramifications of public funded social media.

Blog post here: https://dynamorando.pages.dev/blog/the-public-web/

The most common refrain that I get whenever this topic comes up is "First Amendment" - meaning that public funded social media should not be in the business of moderation; though I often wonder how come NPR, PBS, BBC and so on don't run their own social media websites (based on your deciding flavor of ActivityPub instances.)

I believe the German and Dutch governments run their own Mastodon instances, I don't understand at the moment why other governments don't follow this path.