So, it's entirely unfair to suppose that since people got used to having tap water and so we are surprised if a person can't operate a tap, therefore they should be used to the entire complexity of computation by now.
You definitely _should not_ count machines that aren't actually computers ("digital accounting machines with storage") since those aren't Church-Turing, they're just another trivial machine like a calculator. Instead, compare the other working example we have of full-blown Church-Turing: Humans. Why aren't people somehow used to everything about people yet? People have been around a long time too. Why isn't everyone prepared for every idiosyncratic or even nonsensical behaviour from other people, they've surely had long enough right?
Also, I consider some of this very US centric. In many parts of the world, AOL wasn't a big thing. In many languages, people are used to the fact that important parts of a sentence come at the very end, e.g., the verb, at least in some tenses. Moreover, most important identifiers go from the minor, less important part to the bigger, most significant ones. Why can't we tell users that domains work just like their post address? (As in "street-city-country". And there are even funny ones, like "street-city-state-country" and even funnier ones, like "c/o", meaning it's not the usual addressee. Why are people able to deal with this?) If you're living in a western country, even your own name works probably like this. Why this, oh, it's magic, don't care?
I'd say, it is mostly, because we encourage them not to care. Because we say, "Yes, that's really difficult", where we ought to say, "No, it's really simple and you ought to know." The user is still the person in charge. Pampering and flattering the person in charge into incompetence isn't apt to end well.
I'd say, there's a chance to convey simple things, like, the cloud is not on your local machine, or how a URL is principally constructed. Or that a file is saved only, when you safe a file.
Edit: Returning to the obligatory-car-simile, when I did my driver's test, I had to know the intrinsics of an engine, of the braking mechanism, of the steering. I was tested for knowledge of ad-hoc technical repair. It was assumed reasonable for a driver to grasp, to memorize the details, to minutely describe them, and it was even mandatory to do so in order to obtain a license. However, it was less important to drive a car then (you could do well without this in most occupations) than it is to operate a computer nowadays.
Edit 2: And, to level up a bit, how comes that academics are able to correctly cite a book and page, but are unable to parse a URL – and are even flattered for the latter?