Yeah, there's a very simple reason: the FAANG acronym was coined around 2013 when Microsoft was still in a rut, Ballmer was still CEO, and their stock was still down from its dot-com bubble peak.
So this is specifically a Silicon Valley / Hacker News thing (notably relevant to lifestyle and employment issues).
The rest of the world has been using GAFAM instead, even before 2013. (I've also seen "the big 5" sometimes.)
Reducing competition is one of the goals of a monopolist and anti-trust laws applies to all, no exceptions.
Don't you think there are other companies competing against Microsoft for government contracts like Amazon, Google or even Palantir that includes software?
Also, Apple isn't some "upstart" either.
This analogy is apt in so many ways (in addition to the prevalence of MS software in the .gov setting)