In fact, not only do ghosts occupy a privileged and recurring position within popular culture, but within culture as a whole - in fact all cultures, throughout history, have had their own versions of ghost stories.
The only concept that is more persistent throughout human history is of God (and maybe cats, everybody loves cats). The idea of a God being real is another that fits neatly into the "you can't prove it doesn't exist!" argument we somewhat arrogantly used for the existence of phantoms at the top of this article, but ghosts actually give a little more wiggle room than Gods do. Where almost every deity going has some certifiably impossible actions attributed to them - omnipotent powers and "miracles", mostly - ghosts don't tend to have any immediate effect on the world around them.
We can see that there's not a God making burning bushes talk or whatever, but we can't see the effects of ghosts on the world, because they don't have any! At least not physically, because the concept of the supernatural has imprinted itself onto human consciousness since time immemorial. There are apparitions all over Shakespeare's work (most notably in Macbeth, cos SPOILERS a lot of people die in the Scottish Play); references to ghosts in the ancient religions of Sumer, Babylon, and Assyria; the "gibbering...whining" vapours in Homer's Odyssey and Iliad; the Spiritualism craze of the early 20th century; the fear of Ouija Boards that still exists, even.
The idea of ghosts as restless dead spirits, or even of demons or souls in purgatory, really took off with the rise of Christianity in the Middle Ages, but people were already "aware" of these otherworldly visitors long, long before that. You'll even find evidence in the cave paintings of Horseshoe Canyon in Utah, dated to between 7000 and 9000 BC, which some have taken to depict a Holy Ghost of sorts:
You could argue that the reason ghosts have become so firmly lodged in the collective consciousness is down to the aforementioned prevalence in popular culture, but that would be to ignore all the evidence that people were banging on about phantoms long before even the first Paranormal Activity was released (we know, it's hard to imagine such a time).
That the idea of spooks has been around for so long, even seemingly being immaculately conceived in the Neolithic period where such a belief couldn't possibly have been inspired by contemporary religion, stories or otherwise, is perhaps the best evidence we have for their existence. Or else the Paleo-Indians of 11,000 years ago have just managed to get us to believe a joke they made up millennia ago. The cheeky devils.