Budget's are..things.
I don't have knowledge on things, but allow me to take a guess..
Remember in 2010, we had nearly every single house be nearly a repeat (outside of HoTC & Nightmare? I'd wager, they prioritized on the budgets for Kong and Transformers then.
..and look at what's been going on now, with Nintendo; Jurassic World; Pets; and various projects around the property taking away money that would be used for the event. Alongside how much they spent on Universal Monsters, and you can kind-of see where I'm going at.
...You would've thought Stranger Things would wake Hollywood (And UPR) up, to invest a bit more for budget control. But a part of me thinks it's not only that, but the cost of labor with the rise in most likely date's and hours for the actor groups.
I would not be hard pressed to see Hollywood facing a corner where they do have to cut back on the event this year, and mainly reuse what they got.
Happened in 2010, happened in 2015, and will likely happen this year.