If you have prime, you’re ordering a lot from Amazon. (Because otherwise why have prime) so having prime is feeding the beast unless analyzed with an excessively narrow bounding box.

Whereas if one doesn’t have prime, there’s many other retailers.

"The losses Amazon sustains on Prime’s free shipping and selling goods below cost are how it maintains its monopoly power."

According to this article, if you use Prime, you cost Amazon money.

No, that's not what the article says. What the article says is that if you subscribe to Prime and purchase a certain amount, type, and quantity of goods in some configuration you might cause Amazon a loss.

If you subscribe to Prime in any other way, Amazon might make less profit, but you're not costing them money, you're 'feeding the beast.'

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.

Maintaining monopoly power > losses

Amazon inflates prices to include shipping costs on prime goods, despite the subscription giving free two day shipping. It's most obvious on smaller items that typically only cost only a dollar so, but with Prime free shipping they include the shipping cost in the price.

The customer pays for the prime shipping.