there's a lot of car ads that use bicycles. Why?
Because as Adrian suggests, they're selling a lifestyle, a dream. Most consumer cars aren't actually all that interesting - in fact, they're pretty much homogeneous to boot. So manufacturers sell them as providing freedom, fun, youth, or any number of things which cars can't actually offer.
Even Top Gear knows this. How much of the show is about the car, and how much is about some over-edited action/pop film, contrived humour, genuine gadabout entertainment, and occasional celebrity fawning?
Cycling is a bit of an extension to that - I think a lot of people like the
idea of cycling, but don't want to do it because cycling is dangerous because of all those cars. But hey, if they can buy a car which makes those who do cycle feel safer, all the better... as long as it doesn't actually involve getting on a bike.
There are some excellent car ads though.