While many people do enjoy Pirates and the Haunted Mansion simply for the attractions that they are, they do infact have very detailed back stories that make the experience exciting on a whole new level if you know the story. Pirates might be alittle off nowadays because of the Jack Sparrow Overlay, but if you've ever listened to The Story and Song of the Haunted Mansion from 1969, coinsiding with the opening of the original attraction (and pre Eisner mind you), every room and scene of that attraction makes sense and fits together. Rather than just seeming as if your touring the mansion, you feel like you're with Mike and Karen following the Raven to find a way out of the Mansion. That 25 minute recording featuring Pete Renoudet as the Ghost Host still gives me chills when I listen to it.
I would actually say that The Haunted Mansions backstory is the most ellaborate ever created by WDI...I guess you just never took the time to learn it.
(btw...BTMRR and the whole of Frontierland come in a close second in my book for best background story!!!)
Straight from the creators' mouth, there is no story for the HM other than it's a retirement home for ghosts. That's the beauty of the ride. You can make up a story if you want because the narrative is so loose. Obviously many have, but officially there is no story.