I think another factor that a lot of the great classics cannot really be translated, because a lot of them are as much poetry as anything else. Shakespear is of course an easy example, much of his work is actually rhyming verse. But I came across the same thing with Nietzsche, listening to his work and imagining how I would translate it into English. His concepts and ideas would be easy to bring across, many are quite simple - but in his own words he also plays with the relationships between ideas and concepts using puns and wordplay that simply do not work in any other language. I imagine many Japanese classics would have a similarly high bar. If a work is perennially beloved for its prose, anyone with the skill to write that kind of prose in another language could probably write an original work that would also become a classic.
Though apparently, whoever translates the Name of the Wind into Spanish is an exception...
This is a problem even with classics that are merely sufficiently old, rather than being entirely in a foreign language. "Whan that Aprille with his shoures soote, the droghte of March hath perced to the roote..." is inaccessible for the modern English speaker without considerable investment, but translations, while still being enjoyable, inevitably lose the original's poetry, and even after translation - unless the translation is so loose as to essentially become a rewrite - one still needs to do yet more work to correctly understand meanings of references in the text that have no instantly accessible equivalent in modern culture.
This causes an issue with intuitions about a text: relative inaccessibility and the need for extensive study is common for works that have stood the test of time simply because of their age, and as we encounter this over and over, the very presence of these properties causes us to lean towards mentally filing a work in the "highbrow" category, and the lack of them otherwise accordingly - and thus "this is pop culture" or even "this is popular" become shortcuts for "this is worthless", without one actually needing to do the work to demonstrate the worth or its lack.
However, inaccessibility is neither sufficient nor necessary nor even particularly desirable for a work to be worthwhile; many classics of today were popular culture in their time, and so we must fight the instinct that causes us to think of the two categories as being mutually exclusive.
Though apparently, whoever translates the Name of the Wind into Spanish is an exception...