The shipping fee is revenue until you waive it
If the buyer pays $8 for delivery, that $8 arrives with the order. Waive it and the order costs the same to fulfill while $8 less comes in, so the fee is not a discount on the product - it is revenue you are choosing to give up, order after order, for as long as the offer runs.
The page makes that explicit by printing profit per order twice: $28 with the fee on a $50 order at a 40 percent margin, and $20 without it. The table carries both versions across your monthly volume, so the offer is priced in dollars before anyone starts arguing about whether it lifts conversion.
Where the fee was never profit - you collect $6 from the buyer and hand the same $6 to the carrier - waiving it changes nothing, and the page says so plainly in its note rather than presenting a dramatic number that does not exist.