Carplay: Siri won't open SiriusXM app

What am I missing here? SisirusXm isn't a native Carplay app so I was hoping that I could simply ask Siri to open it. It opens fine on the phone itself via Siri, but tells me it can't do that while I'm driving?! Isn't that the point? Is this on Apple or the Sirius devs? I can understand a visual app (Netflix, Youtube) not opening, but this is no different than Spotify or Pandora really.

Anyone know why this might be?