I'm late, but I think that there is a whole lot of stuff going on. There's no one thing to account for everything...
Terrible Galaxy's Edge Marketing
Instead of saying how cool Galaxy's Edge is going to be and how much fun you're going to have, the messaging has been how much it's going to suck and how much you're going to spend. No one wants to hear about 4 hour lines, shoulder to shoulder traffic, $75 beers or $200 glow sticks. I think the messaging on Galaxy's Edge was all wrong and it's scared a lot of people away.
Terrible Galaxy's Edge Timing
There may have been people who were planning on going when Galaxy's Edge first opened, but there were also people like me who planned on getting one last trip in before it opened. By opening it up early, you screwed with a lot of people's plans and there were probably a lot of people who cancelled all together. Thankfully, I didn't and the expected madness did not ensue, but I can't say that's the same for everyone.
Galaxy's Edge Timeline
Star Wars is a kids movie about space wizards and puppets. The kids who are now adults grew up with the Original Trilogy or the Prequel Trilogy. By overly focusing only on the Sequels, you're not catering enough to the adults. I love Hondo, but I doubt most casual Star Wars fans have even heard of him. This is a theme park universe, it doesn't really have to fit into any timeline. Everyone knows Yoda and Darth Vader, but they're nowhere to be found. There's no reason why Yoda, Rey, Ashoka, Darth Vader, Luke Skywalker, BB-8, HK-47 and everyone else can hang out at Star Wars Land.
Shanghai
Disneyland / International Competition
They opened with 5.6 Million visitors in 2016 and they're at 11.8 Million in 2018. They could surpass Epcot in 2019. Chimelong Ocean Kingdom also opened in China in 2014 and they're already at 10.8 million visitors. They could very well surpass Hollywood Studios in 2019. You got a lot of international parks that are stepping up their game, so if you live in that part of the world, why would you make the trip? The strong US Dollar is also making it more expensive for international visitors even without a price increase.
Domestic Competition
By all indications, Universal has really stepped up their game. Regional parks have stepped up their game too. Regional parks especially have much more reasonable prices and the quick service food is better for less money. A season pass to a place like Silver Dollar City is $115. They have free parking. They have pretty good pizzas for less than $10. It's not just theme parks either, there are probably more choices for your entertainment dollar than ever before.
Potential Culture Shift
What was important to one generation isn't necessarily important to the next. For example, you used to see crowded sporting events, but now you're seeing lots of empty seats everywhere. NFL, NHL, MLB, WWE and MLS are all having problems. We could be something similar here. Perhaps people are more inclined to go different places, maybe somewhere they've never been before as opposed to going to Disney World year after year. There are lots of places to go, lots of things to see, so why not?
There's also the fact that we're seeing an aging population and people having less kids. Especially for those with higher levels of income.
The Recession
The recession is coming or at least the fear of an impending recession is very real. When that happens, people are less likely to spend money on vacations, especially expensive vacations like Disney World. It's also not just Disney that's increasing their prices, but it seems like everything is more expensive nowadays.
Increased Prices, Decreased Services
People don't like paying more for less and everyone has a breaking point. The prices are going up on absolutely everything and they're cutting everything. When people pay significantly more, they expect more. Instead, they're getting less. That's a major turn off.
Increased Crowds, Hitting Capacity, Not Keeping Up with Demand
Magic Kingdom went from 15.4 Million in 2000 to 20.86 million in 2018. Disney was pretty lazy during that time. They should have been adding lots of new rides all the time for all of those people to go to.
It's Complicated
Fast Pass Plus,
Disney Dining Plan, Disney Deluxe Dining Plan, Minnie Vans, Disney's Magical Express, Disney's Genie, New Ticket Structure... Lots of their new stuff is nice. I especially love Disney's Magical Express and Fast Passes, but by making it more and more complicated, they're turning it into work for a lot of people. Not everyone likes to plan 180 days out for their advanced dining reservations or 60 days for Fast Passes or anything else. For a lot of people, they just want to show up and have a great time. If you just show up with no planning, you're going to have a bad time. That's a problem.
Disney World's New Reputation
When they first started raising prices, the feeling was that their product was undervalued and that Disney World was special. I don't think they have that same reputation anymore and I think we're starting to see that here. I think their new reputation is that a Disney vacation is expensive, it's overly complicated, it's crowded, it's hot, it's not special, and everything in the parks is overpriced. I think for a lot of people the magic is gone or at least greatly lessened and that's a problem. Especially at these prices.