Behavioural research consistently finds that most category purchases are repeats. The customer does not re-evaluate the shelf — they scan for the shape they bought last time.
A switch requires two ingredients: a strong enough reason to break the default, and a low enough friction cost to try the alternative. Prize mechanics supply the first; money-back guarantees remove the second.
Brands that treat switching as a media problem overpay. Brands that treat it as a behaviour problem design the incentive first and buy the media second.