Idk...probably because they were forced to read the classics and a lot of the classics are...not fun (and not actually good.), but also only reading and analyzing old stuff makes it seem like new stuff lacks that same depth when that's not even remotely true. But unfortunately, for the most part the only people who get to read and analyze modern fiction are English majors. And I say that because contemporary fiction is usually a higher level class and not one you can just take to fulfill your English requirements and it's not offered at most high schools either. Then you have the snotty as hell crowd in basically any book space who act like nothing except classics and Serious Fiction can have a theme. and I mean yeah there's things like the Hunger Games franchise, but it is YA and still falls into an area of like...teaching young people lessons via fiction. Plus, in my experience (working in a library - although in a small town.), not as many adults read YA as you'd think.
I think that's one of the good things about a series like Dungeon Crawler Carl. It's fiction, it's fun, and it's utterly absurd, but it also very obviously is about something. Even the idiots who get the theme wrong (I'm looking at you conservative men who think that a guy called a compensated ANARCHIST is somehow a conservative power fantasy.) still understand that there IS a theme there and a deeper meaning to the story (the meaning is that capitalism is super bad and victimizes everyone involved, even those who at first appear to have power within the system aka a certain fish family being tortured and killed because their relative refuses to join the literal space fish nazis....I'm trying not to be TOO spoiler-y.). I think it's one of the first popular adult books in a long time that so obviously has a theme. This is something Carl says in book two, and it only escalates from there: "If it used to be okay, but it’s not okay anymore, then maybe you should do something about it. Don’t compare your circumstances with how they were yesterday. Look at how they were years ago. We’re supposed to be making the world… the universe… a better place for our children. If it’s not better, if you’re dealing with cruelty, with neglect, then you should do something about it. So, yeah. Fuck ‘em. Fuck King Rust and his asshole child. If you’re unhappy with your government, then kick them out and set up your own, one that represents the people’s best interests. You shouldn’t have to put up with some loser who’s going to take the people’s money and waste it on games, especially when those games entail killing people weaker than him with little or no real danger to himself. What a pussy. That’s my opinion". - Carl's Doomsday Scenario
It's very hard to read that and not think that despite being about an absurd alien game show, the books *mean* something. I think that's why people love them so much. The theme resonates with them. But we don't get to study things like that in school, and so newer works aren't given the same gravity as older ones and everyone thinks that fiction has nothing to say and is just wish fulfillment.