Look at all those Korean novelas and shovelware on Netflix. There are cohorts of subscribers who remain highly loyal because they're into it. Netflix isn't necessarily swinging for the fences with high brow, popular content that competes with the best studios in the world. Instead, they pump out a wide variety of content that keeps the maximum number of people subscribed.
Apple is similar. They promote features - whether it's Siri, health, privacy, family sharing/controls, etc. - that will strongly appeal to some cohort and keep them on the platform. Then, they incrementally hook you into services until you're buying $1000 devices for the whole family and paying $30/mo for the services bundle. And once you're there, they have you because the switching cost involves turning your digital life upside down.
I'm sure enough people find some small use for the voice commands that it's a good feature to have on the phones.
Amazon is selling the devices at or below cost and hoping that Alexa will make the money (which it doesn’t)