One factor to take into account is that they aren't giving away the gate anymore. Every passholder from the cheapest to the most expensive used to have Fright Nights included - there were a lot of 'free' entries making up those sellout nights.
These days only the higher tier passes have it included, and for everyone else it's chargeable, with passholders having a reduced price ticket. I wouldn't write off this year as a failure for the park - they've obviously managed to reduce patronage, but in the same turn have likely increased revenue - either from 'gate' tickets, or charging more for the passes that have it included. This is the direction we've all been screaming for them to take, so its nice to see that it has worked. Imagine the queues if all the VIPs still had free entry...