On: Public Sans – A strong, neutral typeface for text or display

[legitster]

The key word is "neutral". The government doesn't set a preference for a specific font or organization.

[citizenkeen → legitster]

What is a neutral font?

[legitster → citizenkeen]

If they pick a font, even an open source one, it could encourage people to copy them. Or be making some (very minor) statement about open source.

By developing their own font, they don't set preference for any organization, group, or business.

[snazz → legitster]

They do develop it on GitHub, which I would consider to be a stronger statement than font choice.

[beatgammit → snazz]

Well, nobody said they had to be consistent...

[cbhl → citizenkeen]

If I recall correctly, Open Sans was commissioned by Google.