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.
Places like Disney do the opposite. Fireworks are late so people stay and spend more money on food, drinks, and extras.
Fireworks at most amusement parks, but especially Disney, just gather everyone outside of restaurants and gifts shops, so those can try to start closing up while the fireworks are happening. Fireworks end, everything is closed, everyone takes the hint to use the restroom one last time and GTFO.
A lot of it is also timed for workers. That’s why many places have later breakfast times on weekends.