Volvo has shown that CarPlay is easily integrated into Android Automotive as an app. I have no idea why GM would alienate so many potential customers by not doing the same.
Integrating Android Auto into Android Automotive is even easier than CarPlay, and GM is dropping it as well. It's quite literally a built-in feature of Android Automotive that has to be actively removed.
(Just to keep the distinction clear: Android Automotive == A Google Android-based interface for car infotainment, Android Auto == An API for projecting your phone screen and relevant apps to an infotainment display)
It's 100% about extracting revenue from customers by forcing them to use the manufacturer's infotainment ecosystem and charge for recurring subscriptions to things your phone will do for free (and in an actually upgradeable manner).
Iirc, it’s been said that the reason for them to ditch CarPlay is so that they can add their own infotainment system where they can charge for subscriptions.
It’s not a technological problem, it’s a “we want to extract every penny out of our customers” problem.