Okay, and those things don't go away - nor do we stop building them - if we use buses or trains or planes or boats or teleportation pads instead. What about cars, specifically, contributes to this where other modes of transportation do not?

I can almost understand this for roads (but buses still need those, too!). Literally everything else is entirely orthogonal to cars or the lack thereof; abolishing cars entirely v. switching to electric-only would have zero impact there.