^^Yeah, but with few exceptions (the clowns in Gotham @ SFMM)...none of those parks have the talent, fanbase, or history Haunt has.
Believe it or not, lots of people (both hauntfans and regular guests) come back just to see their favorite monsters year after year.
Haunt has become something bigger than just a theme park Haunt. I totally see where you are coming from, and it's really hard to explain to someone who is "out of the loop" so to speak when it comes to the culture that is Haunt...But I think part of the reason Haunt has become something bigger than just a theme park haunt is the fact things don't change as often.
If they changed things every year, the talent would still be great, the sliders would still slide...but it just wouldn't be the same.