It's interesting because I feel like the popularity goes beyond the obvious 'dangerous, immortal, hot' thing, which is definitely part of it. The appeal for me sits in the permission the supernatural framework gives. When a character is centuries old, they've shed a lot of human hang-ups. That creates a space for exploring desire without modern social judgment—the power dynamics, the obsession, the biting (obviously), it all feels more acceptable within the rules of that world. You're not just reading about a billionaire CEO being possessive; you're reading about a creature whose very nature is to possess, to claim, to crave. That dials the intensity to eleven in a way that feels organic to the story, not forced.
Also, there's a built-in emotional stakes mechanism. Mortality is always on the table—the human's fragility, the vampire's eternal loneliness. That 'forbidden' element, whether it's fear of turning them or fear of being discovered, adds a layer of tension that pure contemporary romance often has to work harder to manufacture. The bite itself is such a potent metaphor for intimacy and violation, pleasure and pain, giving and taking. It's a physical act that can represent trust, submission, or total dominance, which gives authors a lot of rich texture to play with beyond standard scenes.
My personal soft spot is for the older, world-weary vamps who find their 'light' in a human. That contrast between jaded immortality and vibrant, fleeting human emotion gets me every time. It’s less about the smut for smut’s sake and more about how the smut is a manifestation of that profound, chaotic connection between two vastly different beings.