Notably, they are still focusing on AWS and MS offerings, but also doing further market research.
I'm curious about the specifics as to why GCP isn't on the shortlist.
Privacy, compliance, and stability aren't GCP's strong suite (by 'compliance', I mean several types, but to the greatest extent, being able to count on an API you use today existing tomorrow)
Rather oddly, Microsoft has historically gotten this nearly perfect.
I'm a bit sketched out by the increasingly malicious nature of Windows (spyware, adware, etc.), and if that same mentality translates into other offerings, this may be moot in a few years, but for now, Azure+Office 365 are the preferred vendor if you're dealing with data which really needs to proper controls.
(Although I do trust Amazon over Microsoft for the technical aspects of security)
It's not odd at all. Microsoft had the chance to gain experience in this field since its inception (thanks to developing an ubiquitous OS with good backwards compatibility), whereas delivering products and services to governments is relatively new ground for Google and Amazon.