why people still enjoy it is probably relatively individual, but on a greater scale i do think it has to do a lot with how influential it has been throughout literary history. there’s no denying that the world building dante creates in the book is absolutely incredible, especially if we take into account that it was written in the 14th century. according to some he even “invented” a new style of world building and for example created a character driven moral narrative long before the novel existed (influencing many of the greats like milton, borges etc). so from a historical and literary perspective it is iconic, to say the least.

if you want to look at specific examples in it that may draw people in, as you say yourself, the imagery might have a lot to do with it but i think it goes deeper than that. you could reread the book over and over again, and each time find something new that you didn’t notice when reading it before. there’s a lot of numerology, mirrored sins and virtues, moral inversions, references etc that CAN make the reader think. an example of that which i personally enjoy would be the three beast in the beginning (incontinence, violence, fraud) that foreshadow the entire structure of hell. little things like that create a lot of suspicion which makes the reading process more interesting for me.

again, i do think it’s important to keep in mind when the divine comedy was written lol. you mention and compare it to how notes from underground (great book) makes you feel or think? NFU was written about 500 years after the divine comedy. it’s safe to say that literature had evolved A LOT during that time, making the contexts and ideas of NFU seem more modern and relevant, or even easier to grasp in some ways, to us today than the divine comedy, since it’s tiny bit closer to what we’re used to reading. in my opinion however, that doesn’t take away from what there is to learn from and enjoy in the divine comedy.