@Mark3921
It appears that Airbnb assumes that guests check in and out as scheduled unless someone tells them differently.
You have identified what I see as a weakness in the system.
I know when guests arrive because I have to show them where the house is.
For hosts with self checkin this could be a problem if they don’t have a door camera.
I could see a possibility of guests arriving and leaving, then claiming that they were never there, and demanding a refund.
I have written requests for guests to notify me before they leave, and back this up with verbal notice at checkin, and most are considerate enough to do that.
I think it would be better if they were required to formally notify through Airbnb of the exact times of both check in and check out for insurance purposes if nothing else.