I think you misunderstand. It’s normal in US to carry IDs, usually driver licenses. But those are state-issued IDs. They are becoming unreliable when dealing with federal authorities, however, because they don’t prove citizenship. For example, my permanent resident wife has a state ID, she also has a social security card, and other documents, but she is not a US citizen, so her ID she carries does not verify her right to be here. (She has another card for that, which until recently she likewise did not carry regularly since for 99% of needs the state ID is sufficient.)

A passport is one of the few federal IDs we have that also prove citizenship, and probably most Americans, or a very significant number of them, do not have one or did not have one until semi recently. It was about 12 years ago the US stopped accepting state ID to enter the US from Canada, which meant most people could cross that border without passport. Plenty of Americans have either never left the country or only traveled to Canada thus never needed a passport. (Kind of a big country.)

So yes, it is new for them to have to carry passports, which aren’t nearly as convenient as the existing state IDs which fit in a wallet, as well as, kind of a pain in the ass to replace if lost or stolen – it can take months to get a replacement. (Ditto for PR cards; last time she renewed her it took 14 months(!).)

As of a few years back you can now also get a “passport card” which is a federal ID (it is also a REAL ID, for you statesiders). I have both, and I do carry the card version with me.