As others point out, those “losses” are more than made up by the customer lock in effects and market dominance they bring. A sale on item “x” is not a loss if

As others point out, those “losses” are more than made up by the customer lock in effects and market dominance they bring. A sale on item “x” is not a loss if it’s net effect is to bring in massive profits. If there was no overall monetary benefit to prime it would be peculiar for Amazon to keep it.