and yet sony has done something very similar with an app on your iPhone or ipad
Sony has created a control app sure, but that's not integrated with Siri or CarPlay.
Apple has demonstrated at WWDC that while they are more willing to allow integration than in the past, it is still going to be on their terms. That means APIs for specific tasks, much like CarPlay's API where you give it access to your app's audio files, rather and presenting UI. So Apple would need to provide a generic Siri API (doesn't seem likely if they are doing task-focused things), or actually care about this scenario enough to do something about it, which makes no sense to me.
iHeartRadio is a launch partner for CarPlay. Add support for something like TuneIn, and you have local FM/AM pretty much covered. Sirius XM integrated on iOS would cover that need as well. At that point, why would Apple care about the scenario of controlling your radio? Apple is skating to where the puck will be, and it isn't controlling your head unit. CarPlay and the like are about making head units a dumb terminal to your smartphone where it can be flexible, grow, adapt, and have access to cellular data.