If they cared, they would let customers filter to only search items shipped and sold by Amazon.com, and they would come out and publicly announce they do NOT commingle inventory. They specifically removed the ability to filter by "shipped and sold by Amazon.com" (ignoring the fact that with commingling, it doesn't matter anyway).

Since they do not do the above, they obviously do not care. Retail profit margins are tiny, and they make far more on a third party sale while shouldering none of the risk. Therefore, Amazon's best strategy is to appear to care, as long as people continue to shop. And the more third party sellers people use, the better for Amazon, as they simply skim some percentage off of total sales.