Presumably because turning the steering wheel to the left (or the right in countries which drive on the right hand side) is closer to "pulling" than pushing (particularly if you use and under-hand grip on the wheel). Never thought about it before ;-)

'Why' rarely makes sense in questions about English. It's a mongrel language. Things just are what they are, usually for historical reasons lost in time...

Hi Yuta, the word "over" in this context is used to show movement, so we can use many phrasal verbs to show movement, such as: "come over" "can you come over?" which means "can you come to see me"; "Go over" means "revise or review" "fall over" means to to fall from an upright or standing position to a horizontal position" "Move over" "can you move over so that I can sit on the couch with you" and "Pull over" means "to stop the car on the side of the road" "I need to pull over" "Can you pull over?" I hope these examples help, but let me know if you have any questions. Sinead