Many guests leave without checking out - saves time for everybody. Cleaning staff prioritises those rooms that are being checked out that day, to ensure that they are clean for the next night's arrivals. (many of whom appreciate a room well before the official check-in time) When cleaning staff finds an empty room with no belongings, the base assumption is that the guest has left. None of this is something that should be done differently.

If you think there's even a small chance of returning, you leave a DND sign out. At 12:01pm they will knock on the door and enter your room to clean. Don't worry about that.

"Fault" is too strong of a word. You retained access to your room the whole time. You could have done things a bit differently, though, and now you know...