Amazon has a program called Multi-channel fulfillment. But there are significant drawbacks to sellers and marketplaces:
1. It comes in an Amazon box. Large marketplace have started penalizing sellers for that.
2. They don't integrate into fast shipping programs that act like Prime, as an example eBay eGD.
You are right that eBay and Walmart can offer this service, but most sellers will sell in multiple places, and splitting inventory across different facilities is expensive, inefficient, and difficult to manage. Isolationism in this market hurts everybody.
1. It comes in an Amazon box. Large marketplace have started penalizing sellers for that.
2. They don't integrate into fast shipping programs that act like Prime, as an example eBay eGD.
You are right that eBay and Walmart can offer this service, but most sellers will sell in multiple places, and splitting inventory across different facilities is expensive, inefficient, and difficult to manage. Isolationism in this market hurts everybody.