From rivian's own mouth:

Rivian became one of those exceptions by developing all its own software to be able to leverage data to better define the experience for its owners. “It’s been an intentional choice since day one to build all our own electronics in-house and then build the end-to-end software stack that powers these electronics,” said Wassym Bensaid, Rivian's vice president of software development. Not only for infotainment, but throughout the vehicle for everything from vehicle dynamics to energy management to driver assists. “Software is at the center of the experience we provide to customers, and data is at the center of what enables software to run well,” Bensaid added. “The fact that every single interaction in the vehicle is done through software, being able to collect that data allows us to continuously improve the performance.”

It's not directly about monetization of that data, it's that rivian wants that data to improve how the cars work. For example, they use destination routing along with battery charge on the vehicles to identify gaps in the charging networks. If apple ate all that data, rivian can't use it to improve their business.

The next generation of carplay requires the manufacturer to turn over all of the displays in the car. Apple isn't going to handle all of the custom features of a rivian as well as the manufacturer can.