GoKawiilApple CarPlay's biggest strength is consistency. You can step into any compatible car and, no matter the type of display or its size, you'll see the same interface. The apps you use on your phone, along with your contacts, are all accessible. You don't need to port anything or create new accounts to get going.
Drivers don't need to worry about whether built-in infotainment systems are any good, since you can ignore them with CarPlay. Before the the CarPlay and Android Auto era, drivers were stuck with whatever infotainment system the manufacturer had built. This wasn't consistent, nor were many long-lasting: MyFord Touch on Ford and Lincoln cars lasted just five years. BMW, meanwhile, tried to charge $80 a year for access to CarPlay. Navigation was a common problem with older systems. Maps would quickly become out-of-date and sometimes required a costly fee to update.
It made sense for manufacturers to add CarPlay (and Android Auto) support to their vehicles: they could hand over the bulk of functionality to Apple's (or Google's) system while focusing on other areas. Apple CarPlay now supports over 800 different models, so the arrangement has certainly taken hold.
For manufacturers, though, handing over the dashboard to Apple has become a bit of a problem. Electric cars in particular require much more integration between the dashboard software and the vehicle itself. A whole host of features on EVs aren't an ideal fit for Apple CarPlay, including battery preconditioning and manufacturer-specific charging controls. Standard CarPlay sits on top of the car's own software to effectively act as a mirroring app for your phone, and you may need to leave it if you need a feature Apple's solution doesn't support.
CarPlay support matters to drivers. Apple claimed at WWDC 2022 that 79 percent of car buyers wouldn't choose a model without CarPlay support, while a more recent survey suggested losing CarPlay was a "deal breaker" for 55 percent of its users. The consistency makes CarPlay familiar and easy to use. For those making the cars, though, Apple controlling the parts of the on-screen experience we see and use the most means manufacturers have less control and power. Some companies are deciding that this compromise no longer works for them.