they want you to shop with your voice because there is a lot of friction if you then decide that's not what you really wanted. most people if they mistakenly order something with alexa will just let it be delivered, not cancel it.

same with using a mobile app to shop. you have less ability to cross shop quickly because the interface is inherently slower than a mouse and keyboard plus the OS multi tasking features are horrible. plus they get a lot more information about you with their app.

so it's not always that they think the feature is better for you, it may just be that it's better for them.