The second cause is condition. If an inspection turns up something the seller did not know about or did not disclose, the buyer renegotiates, asks for repairs, or walks. That adds weeks and sometimes ends the deal. A pre-listing inspection removes most of this risk.
The third is legal. Inherited homes, separations, and properties with several owners all need clear title and every party's signature before a sale can complete. Sorting that out after an offer arrives can take weeks. Sorting it out before listing takes days.
Joel Dyck identifies these before the sign goes up so the sale runs cleanly through to possession.