The carve out for US Government work is explicitly stated in the statute. Not only does that not create a precedent for others to create copyright-free works, but if anything it makes the case that exceptions to copyright-by-default have to be explicitly defined in law.
OSI approving something is meaningless from a legal standpoint, it’s just some people on the internet. Even were that not the case, creating a license is not the same as renouncing copyright. Which, again, it isn’t clear that it is possible to do under US copyright law.
Edit: to be clear, MIT-0 doesn’t even attempt to renounce copyright. It merely provides slightly broader rights to holders of a license to the copyrighted work.