[velcrovan]

“is there a good reason that the zero isn't dotted in this font?”

Because it isn’t a coding/monospaced font?

Most text/display typefaces don’t have dotted or slashed zeros.

The expectation is that if you have ID numbers etc where you’d need them, you would use a different typeface.

The US Web Design System 2.0 (of which Public Sans is a part) specifies Roboto Mono (which does have a slashed zero) for such purposes. See https://v2.designsystem.digital.gov/components/typography/