Deductions are self-service claims: rather than asking, the customer simply takes it. That shifts the burden of proof to you, and it arrives with a free-text reason code and no link to the incentive that supposedly justified it.
Because researching each deduction is manual and per-item, small balances are written off in bulk — and partners learn that they will be. Automating the match to the authorising claim is what stops write-off being the default outcome for anything under a threshold.