because though it's a popular week for locals, the hotels have lots of empty rooms...that's still before most East coast schools get out so relatively smaller crowds. The big summer crowds don't really arrive until after the first week of June.
We were there last year beginning Memorial weekend...hotel was about 1/2 empty. Parks were busy that week, but due to lots of Florida school groups doing end-of-year field trips to Disney (tons of kids in matching t-shirts...Such&Such Middle School Grad, or Something High School Band, etc.) Made for long lines at the popular attractions -- very glad we had fastpass.
BUT like I said, the hotel was empty...and most of the restaurants had empty tables, too.