If you infect tens of vehicles that's not that valuable. But if you infect ten thousand vehicles, convinced a trusted member of one of the bigger black hat forums it's real and have him vouch for your marketplace post, there should be some buyers for full movement profiles, call logs and address books of ten thousand people

And doing that doesn't really interfere with also setting up and selling proxy endpoints

Yeah, especially since most of these are already available for purchase from data brokers.