Walmart is still 2x the size of Amazon in terms of revenue, and like Bezos said in his congressional briefing, it's easier and cheaper to build and online platform than it is to build out Walmart's existing physical retail presence.
If you want to find a thing to purchase online, you know almost certainly that Amazon will have it. This is not the case with any other e-commerce site. No one has the breadth of products that Amazon has. No one comes close. Yes, I can buy things on walmart.com that are commonly carried in Walmart, but they only have a tiny fraction of the overall selection of Amazon. It's not even a contest.
