I was going to make a quip about how that's because, compared to Europe, almost nobody in the States has bothered to get a passport.. but apparently the percentage of Statesians who have passports has skyrocketed in the last 35 years from ~3% to 51%: https://datawrapper.dwcdn.net/Z9qF8/6/
For any US Citizens renewing a US passport: if you want a national ID that fits in your wallet, you can pay $30 and get a passport card. They are a no brainer upgrade to a passport application or renewal IMHO. Cost is a bit higher due to a $35 application fee if you are getting them separate from a passport book but I think they are still worth it.
They can be used for land and sea entry to the US. They serve as ID on domestic flights and for I9 employment verification.
Many countries technically require you to always travel with national ID or require it for traveling on trains (since they have national IDs, unlike the US). But passports are bulky and American travelers have been taught to leave them in safes or buried in bags where they are hard to steal. A passport card can be kept on hand 24/7 in case a national ID is needed.
In the event you lose your actual passport after traveling abroad, they would save a ton of time at the embassy since you have a form of passport already on you. Compare this to the panicked alternative of trying to get a replacement with a photocopy of your passport (which standard travel advice says you should have for this reason) and somehow getting a birth certificate.
