Not surprised. Amazon has their "free shipping" program which puts enormous downward pressure on shipping pricing all the way back to the carriers.

Non-Amazon traffic, for example, business to business traffic, might not be growing as fast, but Fedex/UPS can charge $50+ or even $200+ for a single shipment - that's more than probably the average lifetime shipping profit made from a single Amazon prime user - in one single business-to-business shipment!

A regular North American business would probably have anywhere from 10 to 100 packages a day sent out via courier/UPS/Fedex.

No problem seeing where the profits come from.

Volume does not mean profit, especially when the volume is trying to push for eliminating UPS and FedEx's profits (via offering free shipping)