From the Bloomberg article :
"Chuck Gregorich, who sells fire pits and outdoor furniture, says turning a profit on Amazon is getting harder. One of his popular fire pits costs $200, of which Amazon takes $112 for its commission, warehouse storage, delivery and advertising. That leaves him with $88 to pay the manufacturer, ship the product in from China and cover his overhead."
I have a hard time sympathizing here. They farm out manufacturing to China and logistics/warehousing to Amazon, and then also lend brand to a marketplace they don't own. Assuming this is how FBA selling works on Amazon, it sounds like the low profits they make are just a byproduct of them not actually doing much work.