The US Government uses a lot of Red Hat. Every thread on every blade of every DoD HPC machine under the HPCMP program. Pretty sure a bunch of the DoE systems as well. I'd look at it as a national security investment: whether you agree with it from a business or engineering perspective, the US Government pretty much runs on contracts with vendors. In that version of reality you need an OS, and ideally you want a US-based OS vendor who will sign an SLA. Ubuntu is in the UK, so enjoys the US-UK special relationship, but still not "made in the USA".