For me, it comes down to this: if I really want to enjoy a piece of music (i.e. close my eyes), or if I really want to commit to a conversation with another passenger, I can do that on a train. In a car, I and/or others will be dead.

The same goes for audiobooks: it may be possible to listen to shallow fiction in a car, but anything that requires true attention and concentration is very hard to follow while driving without putting yourself in danger, at least in an urban environment or at high speeds.