For all but a tiny fraction of Americans, the cost of a passport is a tiny, rounding error expense compared to actually leaving the country. This isn't Europe, where you take a wrong turn and end up in a different country. Here in California, there's a highway you can drive on for 750 miles and not even have left the state (like driving from Paris to Warsaw). And we're just one state of 50. On the diagonal, crossing the continental US is like driving from London to Tel-Aviv.
Nearby, we've got Canada and Mexico, and up until pretty recently, you could cross over those borders with a driver's license. And both those countries are big. On the other sides we have oceans. So for most Americans, the minimum cost of an international flight is the same as the cost for a European to fly to the US ($500-$1000), and a full day's travel each way. Here on HN, we might forget that most of the population makes fucking peanuts, so keep in mind that means that for most Americans, $1000 is a lot of money. Most Americans also don't get a lot of time off, so those 2 days of travel are a significant cost in of themselves.
All told, the lack of passports amongst Americans isn't indicative of some isolationist mindset. It's just that they have no need of a passport, because they aren't taking the kinds of extremely far-flung vacations that would need one, and they know if they need one, they can just get one before their trip.
In addition to the other answers, I'd like to add that the Schengen area, the EU, and the Eurozone are all technically separate, none is a subset of one of the others:
Ireland and Cyprus are in EU & Eurozone but not Schengen; Poland, Hungary (and more) are in EU & Schengen but not Eurozone; Switzerland is in Schengen but neither EU nor Eurozone; Montenegro and Kosovo are in the Eurozone but neither the EU nor Schengen.
In europe we have a kind of mini passport, called person id. Which only works in your own country and other shengen countries. It’s nearly the same cost as a passport (at least in my municipality)
You are required to have a passport (or id) with you (as in, that’s what the law says). Even in your own country. But in your own country a drivers license is usually also sufficient.
But in practice you will almost never be asked to show any of those. In your own country, nor abroad.
That depends on country, in Poland you don't need to carry any ID on you anymore (you're then required to remember PESEL number, and recite it to police if asked; 11 digits, six of those are birthday).
In practice you can get away with not having ID on your person in most countries as long as its reasonably close by. Technically you could get in trouble though so better carry one if you might provoke the police.
Fewer than half of Americans have passports. Many have probably never left their home state, and there are probably a significant number who have never left a 100 mile radius around their homes.
People who regularly travel internationally are not a large or powerful voter base. They can be shit on without hurting a politician's career.
Access that costs thousands of dollars for a short trip that most people simply don't have the spare money for. The median US income is <40k/year, and healthcare + housing costs dominate most workers' lives.
Also, it's not $18/year like a subscription, it's $165 upfront -- money that could be spent on gas, food, medical bills, desperately saved up for emergencies, etc. and won't provide any benefit whatsoever to their lives unless they're taking a vacation they probably don't feel they can afford financially or in their <2 weeks of vacation time.
The US isn't insanely backwards. France hovers at 50-60% of citizens with passports. The UK has similar rates to the US. Italy is slightly higher at 60%. Japan and China have far lower rates.
I think you just overestimate how common passports are.
The US is pretty big and varied. It has more than enough natural wonders to last you a lifetime. Nothing wrong with someone deciding that they don't need more than tat.
$18/yr for access to most of the world.
Yet people say "No thanks. I'm sure the US is great."