Recent updates from Safari/iOS and Chrome/Firefox limit Klaviyo's tracking ability to only 7 days (therefore only identifying 10-15% of abandoners). If a shopper comes back after 7 days, Klaviyo has lost the ability to collect signals on that customer, meaning no abandonment signals are collected.
However, with Audiences, Klaviyo will continue to receive user signals and events indefinitely, even after 7 days on Apple/iOS/Firefox/Chrome. This greatly increases the amount of abandonment events that in Klaviyo, resulting in increased abandonment revenue.