Nowhere is this more clear than in our treatment of human blood. For millennia, humans considered blood a sacred fluid, and ascribed mystical, life-giving properties to it. Aztecs spilled blood to ensure good harvests. Catholics drank wine that they believed (at least in spirit) to be Christ's blood, and that drinking it transferred spiritual power to them. Ancient people spilled animal -- and sometimes human -- blood as offerings since they correctly realized that blood is vital for most living creatures.
But this magical treatment of blood has died out in the first world. In the ancient world blood could not be replaced or exchanged. Now blood is something mechanical, a fluid we can top up like motor oil if you get too low. We can package it like a product in the form of powdered plasma. Taking someone else's blood is standard medical procedure, as is donating your own for someone else to use. Blood's interchangeable nature has rendered its power moot, and made vampires seem more like a biological creature than a supernatural predator. (And with all that blood in donation banks, human predation seems dangerous and unnecessary.) In fact, it's telling that Anne Rice's novels jumped in popularity right when public anxiety about AIDS peaked -- for the first time in nearly a century, people were worried about tainted blood.
But all these changes are paltry compared to the big change: the fact that we aren't as religious as we used to be.
Vampires are religious monsters, sharing more in common with demons than ghosts or mummies. After all, you fight them off with exorcism tools like crucifixes and holy water. And not only are they tempters, their bite doesn't just make you join them, it condemns your immortal soul.
This religious aspect cannot be overstated. In most classical conceptions of the creature the real horror in the vampire's bite came not from death, but damnation. Vampires preyed on their victims' souls as much as their bodies, enlisting them unwillingly in Satan's army. Vampire victims lose both body and soul in a coerced conversion experience. While this likely spoke of societal fears in Eastern Europe -- where people feared conquest and conversion by Turkish invaders - it keyed into a fear of hell that doesn't exist in the modern world.
Medieval and Early Modern Christians had a very personal relationship with Satan. Both villagers and urbanites blamed the devil and his agents for crop failures, disease and animal deaths. The Catholic Church taught that inner turmoil such as sexual temptation or emotional reactions were demonic in origin, essentially creating a worldview where both the internal and external worlds were cosmic battlegrounds. This spurred an extreme religious devotion that's rare in our time - even the most ardent modern Christian would think it excessive to tithe ten percent of their income, recite prayers while cooking or fight in an army led by priests. Hell wasn't an abstract concept, it was an existential dread. This is a society that considered religious oaths like "damn" and "hell" as as extreme curses (literally curses), and would've found demonic stories to be unfathomable as entertainment fare outside morality plays. (Movies like Hellraiser and Drag Me To Hell would've crossed major lines in the Middle Ages and even the Enlightenment.)
This shift in tastes came in response to a declining religiosity in the west, but more than that, it's due to changing Christian doctrine, which tends to be more about carrots than sticks. A 2003 survey found that only a third of Americans believe in hell as a literal place of punishment. That knocks the feet out from under vampires, a creature calibrated to terrify people that wholeheartedly feared damnation and demonic entities.