Due to population growth there are more people (not necessarily by percentage but just more people) in the upper-middle and higher classes. Due to this there are more potential customers that can afford the ever more ridiculous Disney prices. The population of the US has increased around 50% since 1970. That's 50% more potential customers. Plus the countries in South America and Europe have had population growth as well adding to the foreign customer pool. Add in airfare being cheaper in adjusted dollars than in 1970 and it allows more people to travel farther to WDW.
If I'm running Disney, if I can have half the customers at double the price, I'll be more profitable because I get the same revenue with much lower staffing.
As long as enough people that can afford it (or have enough credit to charge to a credit card and file bankruptcy later) are willing to pay they can keep going down this path. Eventually there will be a tipping point when upper class people stop seeing the value proposition and stop paying.
Florida's population growth since 1970 has over tripled.
There's another phenomenon in America. The shrinking middle income class is not just creating a larger lower income class, but there's actually been more people shifting from middle-income to upper-income.
http://www.pewsocialtrends.org/2016...-areas/st_2016-05-12_middle-class-geo-ch1-02/
They base off percentages of the median. Middle is 2/3 - 2x median.
I'm curious as to the growth of WDW attendance from South America. Incomes there have gone up significantly and air travel is much more ubiquitous than when WDW opened.
Pricing x # customers is complicated because the number of customers impacts resort occupancy rates, food & merch purchases. That's why Disney breaks out overall lumped spending numbers in their quarterly and annual reports.
Things change slowly. From 2015-2016 there was a big shift in AP prices, and attendance went down. Then they ran the 13 for 12 pass holder promo (got me with that one

and attendance was way up in 2017 (although Pandora deserves the most credit for that). If prices are 'too high', attendance will fall, but not precipitously. WDW will make some adjustment, or open a blockbuster land, and attendance will go back up.
For me as a pass holder , even though I never got to the parks much then, but the promise of slow times is appealing. I thought I picked a slower time this past Feb, but it was packed! Late October 2016 was similar. I kinda wish I would have gone some this summer when it seemed to be less crowded. Convincing my wife to pass up Ireland, London, and Hawaii for WDW is an impossible task.