This is something that was obvious from the start. If Walmart's leadership thought that bringing in faster shipping services , updating the website, and partnering with a few companies was going to make them competitive to Amazon, they were sadly mistaken. The whole philosophy of Amazon’s success is based on the customers getting what they want and getting it fast. If you don’t have what the customers want, they will not care about your good and fast services. Think that Walmart's leadership is aware of this by now, but they are very slow in the process of doing anything about it, which can cost as a great deal in the future.
https://www.businessinsider.com/walmarts-biggest-weakness-vs-amazon-is-selection-2018-10