For most of Amazon's existence they have been getting the best deal that they can with the available shippers, primarily UPS, FedEx, and USPS in the US. They n

For most of Amazon's existence they have been getting the best deal that they can with the available shippers, primarily UPS, FedEx, and USPS in the US. They negotiated lower rates than the shippers offer to consumers and businesses in exchange for guaranteed delivery volumes. Basically Amazon promised to ship X million packages per week with shipper Y in exchange for "below market" rates. The issues that Amazon has seen, particularly during holiday peaks is that shippers do not always want to continue to lower their rates and that shippers do not always scale up their operations to meet Amazon's needs during the holidays. For example: https://www.latimes.com/business/la-fi-christmas-shipping-delivery-20171212-story.html https://www.latimes.com/business/la-fi-christmas-shipping-de... and https://www.washingtonpost.com/business/economy/amazon-ups-offer-refunds-for-christmas-delivery-problems/2013/12/26/c9570254-6e44-11e3-a523-fe73f0ff6b8d_story.html https://www.washingtonpost.com/business/economy/amazon-ups-o... In response to shippers not doing what they want and to provide leverage, Amazon started to do their own shipping. This originally started as same-day delivery experiments in large cities as part of Amazon Fresh (grocery delivery service). It grew into non-grocery deliveries as a competitive advantage for Prime same-day deliveries and expanded from there. I expect that "Transportation By Amazon" (TBA) where Amazon does package delivery as a competitor to UPS and FedEx will probably start in the next year or two, barring any anti-trust or legal problems.