Booming is a stretch. Husband is a senior economist so I get more info than most I guess. But I digress. Domestic attendance is barely up. WDW is just doing a good job at spreading it throughout the year.
Also I believe I’ve seen that 1/4 of crowds are international so American economy is not the only driver of crowds.
Remember, those announced attendances numbers are trailing indicators. Attendance was barely up, end of 2019. It's possible that attendance has taken a sharp rise in early 2020. We just don't know.
Other factors certainly making the parks *feel* more crowded, maybe especially now:
Epcot may be a park not drawing much resort attendance. It's basically a construction zone, with several fewer attractions than even recently. Test Track is down for the month. Energy is gone and not yet replaced. Innovations are gone. Character Spot is gone.
So attendance typically taken by Epcot *might* be going to other parks.
Disney's budget cutting -- operating with fewer hours, including fewer extra magic hours, is certainly making things more crowded. Spreading people out over 10 hours instead of 13 hours, etc.
And even if attendance is only rising slightly, we start to see more issues of "critical mass."
Look at it this way --- If a given ride can handle 200 people per 10 minutes.. and 180 people get in line, every 10 minutes, then the line should keep moving with minimal wait. If 195 people get on line every 10 minutes, the line should continue to be minimal.
But if 210 people get in line every 10 minutes, although it's only slightly more, it can cause an ever expanding wait time.
Attendance has been increasing year by year, but Disney World has actually done very little to ADD CAPACITY. Literally, to add more physical room to spread people out, and to add more attractions to soak people up. Animal Kingdom added some capacity with Pandora. DHS replaced only rides with new rides -- to attract more people, but DHS didn't really add physical or ride capacity. In fact, some high capacity attractions are long gone, replaced with lower capacity. (Backstage Tour, Lights Camera Action, Great Movie Ride -- could all soak up TONS of people). Magic Kingdom's capacity has been pretty stagnant for a few years now -- the Tron coaster should help in terms of ride capacity. But with reductions in entertainment, you're actually currently at reduced capacity. No night time parade to soak up people. No Muppets in Liberty Square.
Compare the 4 parks down to 2015. In 5 years, how many of the parks have actually added attraction capacity and/or physical space? AK added a little with Pandora. DHS lost a lot of capacity during all the construction, but I'm not sure they are actually sure whether their current capacity is any better than circa 2014. Epcot WILL add some capacity over the next couple years, but right now capacity is REDUCED compared to previous years. And Magic Kingdom is stagnant.
So even slight increases in attendance can overwhelm the parks without increasing capacity.