They also have budgets
So even if they see the potential of these events making money they might not be allowed to spend money to make it.
I doubt Knotts, Disneyland, Sea World and Lego Land would all run events every year in the slow period and not be making more then if they had nothing.
The coaster will bring people in for sure and really I am sad for it not to be out now because I'd love to see how it affects crowds but now its in summer and I feel like most the hype will be gone by then and crowd levels will remain about the same. Which is why you give them something else to do along with the coaster
Also Fan fest worked out but.....a new event would not? Grinchmas and HHN bring in the most amounts of people and are centered around....an event.