I think Walmart is trying to take a bite out of Amazon's market share when it comes to ecommers and third party sales. A few years ago I applied to Walmart as a third party seller and was rejected without much of an explanation, this was after I was established on Amazon. The other day they reached out to me to join and offered me $500 in advertising spend.
I don't know if this applies to anybody else here, but if you wanted to get into Walmart's market place and were rejected in the past now would be a good time to try again. Apparently they have about 1/13th the merchant competition for any given category when compared to Amazon. They are like 7% of ecommers in the US, where Amazon is something like 38%. Doing the math it seem like a solid strategy to join. Also, there's zero monthly and signup fees, they just take a percentage of sale.