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.

Although the GP smacks of snobbery, I think it's mistaken to credit the enduring reputation of Shakespeare to his smutty innuendos alone. Surely the reason that Much ado about nothing is still being read today is the sophisticated battle of wits between the protagonists who are lovers, helped along by Shakespeare's uncanny ability to characterise. It is true that some of his early plays such as Titus, Henry VI and Comedy of errors rely on simpler means of entertainment, but hardly anyone consider those to be his best works. (Incidentally the also early Love's Labour's lost ranks among the most complex utilisation of the English language before Joyce, a play that cannot by any stretch of the imagination be considered 'popular'.) The hermeneutical problems of Hamlet, Lear and Macbeth are legendary, that's not to mention the even more mysterious late plays. Even Shakespeare's contemporaries recognised his difficulty and extorted people to "Reade him, therefore; and againe, and againe" in the preface to the First Folio. I think it's an error to over emphasise the more mundane aspects of his art when the more extraordinary aspects are what attracted people in the first place.

Oh, absolutely it's not due to his smutty innuendos alone - indeed, it is rather despite them. My entire point, though, is that (at least some of) today's classic literature is the smut-ridden pop culture of past generations, and it is a mistake to sneer at present day works merely because they are pop culture and contain boobs. If OP has a stronger case to make for some particular work's artistic merit or lack thereof, they should take the trouble to actually do so (I do note others have in fact responded to defend the show's merits, despite OP not even trying to make a case for it lacking any, so certainly there is debate to be had), as that is what separates an opening for debate from a sneer. As it stands, however, the original question boils down to "why do talented people devote effort to smutty pop culture?", which, well, my post.