Every car I've had with SiriusXM also supported HD Radio. Low end cars tend to have neither, or only as a premium upgrade

That doesn't match my experience at all. Every car me or my parents have owned since the 2008 Honda Odyssey has had satellite radio and no HD Radio. Even relatively low end cars (what passes for low end in the United States for the past decade, like a Toyota Yaris) have satellite radio, and I've never been in a car with HD Radio except that one time I took a ride in a friend's Mercedes S class.