1. Most cars are Bluetooth enabled, and many old ones have aftermarket systems that are.
2. Most people listen to music at their desk with their computers
3. That does seem a bit of an issue, but part of the point of the AirPods
http://cars.axlegeeks.com/d/f/Bluetooth
yes, there are 11 pages but if you click on say Dodge and filter by 2016 you'll find only 3 high end vehicles with base trim on bluetooth. This means people actually need to choose Bluetooth which sounds crazy to us why they wouldn't but most people have no idea.
2) Most people store their music on their phones though.
It was on sale, so it was cheaper than what you see there.
I have pretty good experiences with it so far. It would also solve your rental car problem!
EDIT: found it - https://www.amazon.com/dp/B01HQ0UVTG?psc=1