If the goal is to simply publish statements, the press already exists for that. The value of a platform like Twitter is in the network and communication. Twitter already has politicians and official accounts from around the world, and millions of users. I don't know how a particular state-owned platform could replicate that... and let's not get into the technical acumen that government contracts lead to. Remember the debacle that was the Obamacare website right after launch.

And on top of all of that, people will still complain that their tax dollars are being used rather than existing public platforms (Twitter, Facebook, etc.) Whichever administration puts it up, the next administration of the opposing party will call it waste and propaganda and burn it down.

An RSS feed is not expensive. As one example it'd be great to have RSS feeds for e.g. the US Forest Service or Bureau of Land Management about camping/hiking conditions, wildfires, etc.