It’s not their software. It’s Google’s. It’s Android Automotive (not to be confused with Android Auto, which is an entirely different product).
I’ve not used Android Automotive yet, so I can’t speak for how well or poorly this works for people in Google’s ecosystem, but it sucks for people in Apple’s. And GM is an US company and Apple is half of the US smartphone market.
Voice integration for Apple’s phones blows without proper CarPlay support. It’s also pretty rough if you have iOS apps that have not been ported to your head unit’s OS.
I wish GM did what Volvo and other manufacturers are doing. Embrace Android Automotive, because the vendors who have been making head unit software have blown for years. Let Google give you a nice stable core OS… but THEN allow projectors experiences like CarPlay to passthrough to AA.