I wonder how much the decline in quality of Amazon's marketplace has affected other parts of the company's business including Alexa. I remember a time when, if I wanted to buy something online, I'd just buy off Amazon without shopping around. They almost always had the best price, their shipping was fast, and I trusted the quality of what I received. In that world, I could see myself saying my shopping list out lout to an Echo to make things easier.
But in Amazon's current free-for-all marketplace, I would never do that. Now I typically check traditional big box stores first, and only go with Amazon if I can't find what I need elsewhere.