I don't think they tried hard to create an experience user would like. Their shopping features is honestly very lacking.
I think Alexa was just because of Amazon's norm of spending very high on R and D. That was the reason AWS was born. No one thought people would pay something like 10x just for consistency in cloud, but here we are. One AWS could cover 20 Alexas.
I'm not sure there is a good means for buying over voice only, and I'd argue it's only possible to know now that users overwhelmingly prefer digitally handling the product (title, pictures, description, reviews) before making even repeat purchases. Similarly, I'm not sure Amazon could convert consumers to a tablet-based purchasing device like they envisioned Alexa; we all have smart phones and tablets already.
e.g. I order a particular soap/shampoo or coffee beans every few months. If they had tried recognizing it, they could actually have improved the experience.
I think Alexa was just because of Amazon's norm of spending very high on R and D. That was the reason AWS was born. No one thought people would pay something like 10x just for consistency in cloud, but here we are. One AWS could cover 20 Alexas.