Owning land doesn’t mean you can just build whatever you want whenever you want, especially if it’s open to other people.
Most of the permits are actually notices of commencement filed with the county, typically Orange County since that’s where most of the built portions of Walt Disney World are located. These aren’t really permits but notices that work is being done.
The permits recently posted in this thread, the ones that often show the larger site, are water management permits. Florida is divided into five water management districts that are responsible for protecting Florida’s water resources, including flood management. These are required when the water management plan of an area is being modified. They required civil engineering design but for buildings only really involve their size to know what is an impermeable surface that’s going to create runoff during rain events.
Building permits are required for the actual construction and demolition activities. These are issued by the Central Florida Tourism Oversight District (formerly the Reedy Creek Improvement District). These are the permits for the actual construction based on the detailed construction drawings developed by the architect and engineers.