Dave drives unless it is his turn to drink....he likes to drive.
I don't mind because I drive nearly 2 hours a day for work. My friend always drives when she and her husband go places because she thinks he is a bad driver. She actually has bad road rage, drives overly aggressively and I really dislike driving with her, but she wears the pants in that family.
Probably some couples do it because it is her car or she likes to drive, some do it because she is a control freak. Hard to tell which.