The short answer
Typically due to newly discovered risks, mortgage refusal, or renegotiation fatigue.
For a seller, a late withdrawal is rarely about the buyer changing their mind on the property itself. It's almost always something that surfaced during the process, whether a risk neither side had visibility on, a declined mortgage, or simply running out of patience for repeated renegotiation.
Why this matters for your purchase
This is the kind of thing a PropM8 Scan is built to show you early, before solicitors, surveyors or lenders are involved, while walking away still costs nothing.