[GMoromisato]

I think this is a great question! There are also many good vampire movies.

All I can think of is that zombies and vampires are so deeply engrained in our stories that they are merely part of the setting and the real movie is about something else. It's like saying why are there so many movies set in New York?

If this theory is correct, then it also explains why we can have lots of alien invasion movies but only a couple of good Alien movies.

[krapp]

In preindustrial societies, "vampires and zombies" (which didn't really exist per se before being codified in modern media) represented fear of disease, death and the unknown and occult aspects of the natural world, and embodied pervasive fears of hidden Satanic influence on the community, of both cultural and physical corruption.

After Bram Stoker essentially codified the vampire for the Western world, they also came to represent the raw power of sexual desire and the corruption of violating Christian taboos in Victorian age England. Zombies didn't really exist as a thing in pop culture AFAIK until Night of the Living Dead, although folklore has plenty of examples of revenant spirits and demons that attack the living, hard taxonomies like "vampire" and "zombie" didn't really exist, just as the distinction between "ghosts", "elves" and "trolls" were blurrier before Tolkien.

Nowadays, there aren't many primal or deep cultural fears in Western society that these monsters can effectively inhabit, so they mostly exist as pop icons and symbols of themselves. Although I have seen the "zombie as the dehumanization of capitalism" and "zombie as manifestation of popular violence." Mostly zombies are zombies because zombies are cool, and vampires are vampires because vampires are cool, and that's the end of it.

Vampires, zombies and aliens are flexible because they don't really exist (aliens probably exist, but they don't exist here) They have a vast amount of folklore to draw from, and can be dropped within almost any setting and motif without much suspension of disbelief.

This isn't the case for dinosaurs. They were real, they were animals, they were big and there just isn't as much to work with thematically, and you have to work harder to justify the presence of dinosaurs in any setting where human beings also exist. You can't really tap into fear, sex, body horror, political intrigue, cool fight scenes, etc. with dinosaurs the way you can with the rest. You can't update dinosaurs for the modern world the way you can vampires, zombies and aliens.

[IAmBroom]

Your point about vampires and zombies being modern isn't true.

The notion of the "revenant" - a corpse reanimating to wreak havoc on the living - is so ubiquitous that occasional burials across the centuries and globe involve the body being place upside down (presumably so they dig the wrong way), with heavy stones in their mouth, or staked.

[krapp]

Yes, I know. I thought I mentioned that in my comment but I guess I wasn't clear.

The modern archetypes of vampires and zombies as they currently appear in media and popular culture are modern in origin. Yes, undead spirits and revenants and the like appear throughout folklore, but all (or very nearly all) modern depictions of vampires originate with Bela Lugosi and Bram Stoker, or pop culture references proceeding from that (such as White Wolf games) and all modern zombies in media originate with Night of the Living Dead.

[47282847]

I’d argue Zombies and Vampires are an archetypical trope of the human Shadow. The narcissist, the undead that consumes other humans.