... is that that Amazon doesn't do more "push advertising" through it.
I get email and text message alerts when, for example, an author I "follow" on Amazon puts out a new book.
But my Alexa speaker usually only throws purchase proposals at me when I've actually asked for something.
For example, I have Amazon Music Unlimited on one of my Echo Dot speakers (got a steep discount offer on it years ago, for one speaker only). Occasionally, when I ask a speaker in a different room to play a song that's not included with Prime Music, it will tell me that song is only available via Unlimited, and ask if I would like to upgrade my Unlimited plan to the family plan.
But it doesn't come at me with "we're running a special on electric dog polishers today, would you like to buy one?" It only does something like that if I ask it a question which might plausibly be interpreted as asking if Amazon sells electric dog polishers.
Given the price point of the Echo line of products (at the moment, the previous -- third -- generation Echo Dot is on sale for $19.95, and I think the new one is $30 or $35), I'd expect a lot of "special offers" advertising. In all the years I've used Alexa, I've probably used it to buy something two or three times; I think all of those were from when I've asked it to tell me about Prime Day deals.
By contrast, my Amazon Kindle (sold at a discount if one allows "special offers") tries to sell me something via a splash screen whenever I open the cover, and with banner ads at the bottom of various non-in-book screens, and with related/recommended plugs on the home screen and at the end of every book.
I suppose one reason might be that, while Echo/Alexa will work without purchasing a Prime membership, it's a lot more useful with that membership, and therefore Amazon may see the incentive to keep paying for Prime as the main revenue center for the product.
But, then, I confess to not being sure how Amazon is making money on Prime itself, if my family is typical. Prime easily pays for itself several times over in shipping cost savings, and that's before the included video streaming, music streaming, no-cost-added Kindle e-books, etc. I suppose we probably order more stuff from Amazon now than we did when we paid shipping, but not that much more.