Most European countries are also like 1/500th the size of the USA though(exaggerating a little bit). Things are much more spread out over here, and from what I've seen we have bigger streets that can handle more traffic whereas a lot of European places have preexisting structures/buildings that prevent streets from really getting any bigger.. Like, I figure that probably went into the thought process when people decided whether or not to invest more in public transportation. If you can't make your streets bigger you probably need to incentivize people to not rely on the limited space of the roads.
I live in the USA and went 3 years without a car and had no issues getting around via public transportation. It just depends on where you live. The USA isn't the same everywhere you go, ya know?