This happens when the maid event comes up when you first open the game. If so then the maids cleaned up all the messes that had accumulated up to the point when the event was generated while the game was closed. However they missed all the messes that appeared after that, but before you saw the event.

So it's something like the following time frame:
- game is closed
- wrappers, dirt smudges, and socks are placed by the game over time
- a random event (in this case the maid service) is generated (while the game is closed)
- more wrappers, dirt smudges, and socks are placed by the game over time
- game is opened and the event pops-up on screen
- player selects to have the maid service clean up, and maids clean up the first messes made.
- maids finish, but leave the player to clean up the remaining messes.


I hope this clarifies it.