You could similarly say that Europe is huge, or that China is huge, or that the whole planet is huge, and therefore the people living there must need a vehicle. Except, most people dont leave their local area all that often, and when they do, theres nothing that inherently requires that the vehicle used to do so much be individually owned. This isnt to say that nobody needs a car, obviously if you live way out in the middle of nowhere, running transit might not be so viable- but that does not describe how and where most people live, even in the US, and for the majority that do live in urban areas, the size of the whole country is irrelevant to if they would need cars if we just built the proper infrastructure.