Just off the top of my head.
And doing that doesn't really interfere with also setting up and selling proxy endpoints
Also typical Android permissions still apply. The user would need to grant the malicious app contacts, call logs, etc permissions.
The only valuable thing there is the relatively 'clean' mobile connection... and this malware's dropping a residential proxy endpoint on the headunit to take advantage of it. Bonus points if the headunit is always connected and always powered up to a +12v rail in the car, that's free and always-on real estate!
Otherwise any car sitting unused for a week or two would have a dead battery.
They do not stay in low power for weeks. Car batteries are really not that big, and cranking an engine takes some amps. I had a Subaru crosstrek that was recalled because their cellular modem was drawing IIRC 10ma 24/7, which would kill the car if it sat 3 or 4 days.