This is likely to protect landlords from tenants who would break shit during their stay and then claim it was broken before they showed up to get a refund.
Some things you simply don't notice at first sight (e.g tiny painting particles falling from the roof, cockroaches, a broken dishwasher..).
If Airbnb's review system were honest, this wouldn't be an issue, probably. In my experience, hotel reviews are magnitudes more reliable.