For example:
Bob Smith 162 Portsmouth St Denver, CO 42348
Encodes the city in both the zip and city / state, allowing either to be wrong. If 162 doesn't exist on that street, it's possible they can correct it based on the name. If it's Portsmouth Ave not St, they likely can figure that out.
None of that flexibility exists in URLs. A single mistyped character or misspelling and you are going to the wrong place with no way of getting where you want (without search engines).
It's a system which works very well for machines, and only passably well for error-prone humans.
But I don't know if it explains why people don't understand URLs. Physical location addresses are no more complicated than URLs (with the exception of URL-encoded blobs in URLs, which are not usually human-readable). That said, I don't usually talk about this stuff with non-tech types, so maybe the average person does understand URLs more or less.
https://news.ycombinator.com/item?id=8907301
Compared to "real-life addresses", URLs are an absolute pleasure to handle and understand; which naturally raises the question of why so many people seem to have trouble, or are suggesting that others do, with URLs? It's just a "virtual" address, in an easily-parseable format for identifying a location in "cyberspace". Perhaps its the "every time you put an intelligent person in front of a computer, his/her brain suddenly disappears" syndrome (for lack of a better word)?
The advocacy of search engines instead of URLs is also not such a great idea; sadly, search engines like Google today do not work like a 'grep' that lets you find exactly what you're looking for, do not index every page (or allow you to see every result, which is somewhat equivalent), and the results are also strongly dependent upon some proprietary ranking algorithm which others have little to no control over. If relying on links and having them disappear is bad, relying on SERPs is even worse since they are far more dynamic and dependent on many more external factors which may even include things like which country your IP says you're from when you search.
Search engines are definitely useful for finding things, but as someone who has a collection of links gathered over many years, most of which are still alive and yet Google does not acknowledge the existence of even when the URL is searched, I am extremely averse to search engines as a sort of replacement for URLs.