That only tells me which one will exist longer, not that "Apple's plan works". I've genuinely seen zero people deliberately use Siri (on iPhone or Mac) over the past 5 years. Apple is certainly losing money on Siri too.
If you look at Siri in a vacuum, you're almost certainly correct that it isn't a moneymaker. But Siri isn't in a vacuum. It comes with a device with an average cost of like $1000. It may not necessarily be widely used, but the ones who do use it are highly likely to remain in the Apple ecosystem and use other products and services that are highly profitable.
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 was one of those zero people until i realized i can tell Siri "add an appointment with Blahblah next tuesday at 11", it will actually understand that and it takes less time than using the calendar interface.
I'm sure enough people find some small use for the voice commands that it's a good feature to have on the phones.
