Guys can be strangely insecure about being "a man". If you tell yourself that you're a manly man because you're into cars which is a manly thing, then when a woman is also into that you either have to reject the uncomfortable idea or start asking yourself some more difficult questions about what being a man really means to you.
Although I'm a man I'm not an expert by any means but that's my read. Could be just plain simple misogyny as well.