We don't understand it either @Mika339. If the guest checked in and was met with a dirty space or a discriminating host, that is one thing. But a lot of these guest-never-checked-in-reviews are from people who never even boarded the plane.
On the flip side, how are you supposed to rate the guest on cleanliness or house rules when you never actually hosted them. Maybe if we all started to give these guests 1-star reviews would Airbnb realize the true trouble of these policies.