I've been saying Universal has backed itself into a corner on relying so heavily on IPs (and deploying too many of them at once versus metering them out) for years - literally once it became clear that the event was going to rely on Walking Dead-level phenomenons to grow year-over-year attendance exponentially. That sort of trajectory just isn't sustainable when you don't have enough red hot IP to drive that sort of interest... and now it's even harder with FOX properties out of reach.
You have to remember there are two types of horror IPs that Horror Nights deals in: the ones that have an evergreen, perennial appeal to people who *don't typically consume horror content* (let's call them Tier A, the ones most heavily featured in advertising), and those that are targeted specifically at horror consumer fans (Tier B). Ideally, you have a mix of both to appeal to every demographic... but there are only so many Tier A's to go around.
To break it down, here's how I see it:
Tier A: The Walking Dead, Stranger Things, Ghostbusters, The Exorcist, Freddy, Jason, Leatherface, Michael Myers, Chucky, The Shining, American Horror Story, Scream, IT
Tier B: House of 1000 Corpses, The Cabin in the Woods, Trick r Treat, Poltergeist (arguably), Evil Dead, Insidious, Hellraiser, Candyman, From Dusk Till Dawn, The Thing
There aren't many Tier A's left... so where does that leave the event?