Alexa was never supposed to make money by itself. It was supposed to do two things, collect information and lower the barrier to buying things.
They must have either collected enough data to lower the value of collecting any more, or they have realized that people got over the novelty of asking Alexa to order more dog food.
My guess is the latter, because buying anything from Amazon now requires 15 minutes of research to make sure it's actually what you want and not at some ridiculous marked up price. I wouldn't trust Alexa to pick the best result on the first try.