Tesla also started doing their "iPad with a car attached" thing before CarPlay was released in 2014.
Arguably they could have switched over at some time, but they're doing well enough that they haven't felt the need.
But I'd be surprised if there isn't a Tesla somewhere in the bowels of Musk's volcano lair that has CarPlay running, just waiting for the right time to release it as a software upgrade option (only $1000!).
Address book syncing is the main issue. I want my contacts on my phone. So taking phone calls gets a bit awkward, though with Siri getting a little better it’s sort of doable.
Other than that it’s the constant re-typing of destinations from the calendar.
Here’s a fun tip I learned recently - you can press the share button on your phone and send the location to Tesla. This makes copying addresses from calendar or anywhere super easy