It's not like this is a hard problem to solve more than adequately with open and more accessible alternatives.
[1] https://scholar.google.com/scholar?q=dyslexia%20arial%20font...
High-definition screens (such as the iMac retina display I'm looking at presently) and many e-ink devices hit 200+ dpi (200--300 is not uncommon for e-ink), which is the starting point for many laserprinters, though those can go to 600--1200 dpi. Monchrome vs. colour will show some distinction in clarity (monochrome effectively has about 3x greater resolution in displays given three-colour picture elements (pels).
My own experience is that I much prefer serif to sans-serif fonts for any substantial reading, though labels and titles may read better in a sans font.
State's decision here seems quite flawed.
Given that Calibri is Microsoft Office's default font ...
... and that Mobile has vastly overtaken Desktop in number of devices (by roughly an order of magnitude) ...
... then it may well be that both Microsoft and the State Department are optimising for reading on mobile. Which could be defensible, I suppose.
Though a far better practice would be to adopt a flexible document standard (say, ePub or HTML, though they're of course not unrelated), which will then adapt to appropriate media characterstics and, say, display in a sans font on small mobile devices and serif in print or large, high-def devices and displays.
(Note that "large" and "high definition" are not necessarily identical: a projection display is large but often not especially high definition. Likewise public signage and the like.)
Edit: As this 2012 NNGroup (Jakob Nielsen) suggests: in "Serif vs. Sans-Serif Fonts for HD Screens". Though the piece notes that with high-definition displays of 200 dpi and above reasons to avoid serif-based fonts are mooted, there's still no clear argument for them either:
Almost all mainstream printed newspapers, magazines, and books use serif type, and thus people are more accustomed to reading long texts in this style. However, given the research data, the difference in reading speed between serif and sans serif is apparently quite small. Thus, there's no strong usability guideline in favor of using one or the other, so you can make the choice based on other considerations — such as branding or the mood communicated by a particular typographical style.
<https://www.nngroup.com/articles/serif-vs-sans-serif-fonts-h...>
(I note that as a strong fan of serif-based fonts for long-form works myself.)
Anecdotally, the most pressing concern I made to management during my career only ever made its way up two levels in the corporate ladder, not including my manager. I have a feeling the State Department is even more rigid with communication flow.
This is amongst the few defensible rationales I can conceive of. The OCR argument offered in the Birdsite thread seems ... weak at best.
(As I've noted in another comment.)
Nobody at the State Department is diving into the intricacies of font licensure.
I'm saying that a decision should be made by weighing pros/cons by someone qualified to make them. If that's HN-y, then that sounds great.
It doesn't sound like how you described this process is anything short of incompetence or "phoning it in". Which, I'm sure is a valid explanation for how they ended up deciding it. But, I'm using the word "dumb" in not a literal sense. It covers both incompetence and laziness.
Also, if you are deciding on a font to be used widely. One of the key aspects is exactly the license. It describes the conditions for its use. If your job is to evaluate which fonts to use, and you don't consider the conditions for its use, then yes, you are incompetent in that decision. And its not "intricate", its the bare minimum expected.