Smartphones are getting increasingly well-integrated into the car's stereo, though - especially in the Appleverse.

From a contingency planning perspective, even if their business is healthy now, they might also want to hedge against a long-term decrease in private car ownership. We're seeing quite a few trends that point in that direction: increasing use of ride share services, self-driving cars, wealthier folks moving back into the cities, increasing cultural interest in moving away from motorized transportation as the default, more remote work.

That's definitely changing as more and more cars are shipping with Android/Apple Auto. Even if it is slightly more effort to pair your phone once, for most people once paired they don't have to fiddle with it again beyond launching an App.

For more power users it's trivial to setup a Tasker/Llama/Automate rule to launch your preferred music app when paired to a particular Bluetooth device.