Well in a weird way the government already provides this just not in the way that aligns with the citizens intent. Facebook originally project lifelog was a government project that came out of Stanford SRI. The other side of that coin is that legally being a non government institution they can coerce FB into censorship or controlling the narratives. Google was also a government project to learn birds of a feather patterns of citizens around the world. They still receive a lot of tax dollars and effectively free real-estate. I doubt that golden goose is going away any time soon meaning that they are not going to create something that is officially a .gov social media site as they would not be permitted to censor or control narratives and the tax burden would be massive without going through government specific VC's such as In-Q-Tel.
This discussion [1] had some ideas that might work from distributed infrastructure but would still increase the tax burden. at very least for those of us that can use email as an alternative to corporate capture portals
Of course, there's drawbacks: take the usual problems people have with say, getting their google account cancelled that you see posted here. When those problems are in the single silo of a Federal ID system, even with the presumable mechanisms they'll have to deal with that; its still going to be worse. Google doesn't ruin people's entire lives; losing your FedID might.
There is no requirement to do so.
If you are a US citizen and want such a system to be made, you need to lobby your representatives in Congress to pass a law for such a system to be created and funded.
Also, most Americans definitely wouldn't prefer a platform run amok with Nazis, racists and conspiracy theorists, which any platform run under First Amendment rules would have to be. Most people have no problem "being who they are" on the mainstream internet anyway.