The juxtaposition is honestly so, so important and so masterfully executed. It controls and balances the tone. It's far more memorable than most works trying to be entirely serious and Professional. It's frequently used to direct the audience's attention, like in GtN where Harrow quoting Teacher just lays out huge swaths of the plot pretty directly, but on a first read we don't have quite enough context to understand what we're looking at and then immediately get distracted by Gideon's "Surprise, my tenebrous overlord! Ghosts and you might die is my middle name!" Sometimes the humor is used to disguise lines that should garner more suspicion, too, like she's not quite the only one who says it but it's weird they still have a concept of middle names tbh? And of course the infamous None House with Left Grief, which really SHOULD be just as glaring as quoting Annabel Lee, especially with both present rather than just one or the other. So many just don't give the same consideration to "lower" references like memes or modern things that they do to "higher" "classic" art—which is textually acknowledged and played with in the way Blood of Eden names equally preserve both.
And yeah, it's so deeply also how authentic and human it makes everything. It's the way you can feel through every page how much passion Tamsyn Muir has for this story. It's not an unfiltered experience, but it still manages to feel like it in ways that really matter, and that takes so much skill to do with such intention.
It's vital to just how special these books are, and while of course I wished more people who turned up their nose could see that, I'm so grateful for how many people started out with mixed to negative feelings about it only to fall in love and understand by the end. Everyone who found Gideon's jokes jarring and intrusive in early GtN but by this passage was emotional about and grateful for Cheap Mustache Rides. I hope the impact it makes spreads and gives us more works that feel like this in the future, because it really is so wonderful.