It's specifically timed: you get up and get dressed for the free breakfast, get back to your room and you're like, "Well, I'm already up and dressed and everything, I might as well hit the road!" And you leave, conveniently leaving the room available for Housekeeping to clean for those early arrivals.
Amusement parks will do something similar: time a fireworks display in a central-ish area near the end of the night. Everyone comes to the fireworks, they end and everyone looks at tl the time and is like, "Well, there's just enough time for one more ride / snack / set of games", and then we'll have to leave," ignoring the way you've been collected to a central(ish) location and primed to leave, making the job for closing security much easier.