As far as I'm aware there are no complete implementations of OOXML other than Microsoft Office, and given the complexity of the specification and the huge gaping holes, it is unclear if it ever will be, or if it is even possible to implement for parties other than Microsoft without reverse engineering large chunks of Microsoft Office.

Until there are other complete implementations, calling it an open format is pretty much a bad joke.

> I just don't think LibreOffice stands up to MS Office as a product

That may be so. But a government has many other requirements than the day to day use. They also, for example, have archiving requirements (with timelines measured in decades) that are hard enough to deal with without the risks incurred of locking documents into poorly documented formats only fully supported by a single vendor.