Mass transit doesn't really work in US suburbs because everything is just too spread out; it's not economical, nor logistically effective, to build subways to subdivisions.
But even in built-up cities, Americans cling to their cars just like they cling to guns and religion. Look at all the uproar in Manhattan, NYC, where they're taking away street parking and putting in protected cycling lanes. People are upset at this "attack" on cars, and somehow think they deserve free places to put their personal vehicles. If you look at another highly built-up city for comparison, Tokyo, they don't have this problem. There is NO street parking; it's all paid lots that cost a fortune. In fact, you're not even allowed to buy a car there unless you can prove you have a place to park it! So most people get around with subways, trains, walking, cycling, and taxis.
The bottom line is that it's cultural: Americans just don't like public transit and don't want to fund it with their tax dollars, but they do want to subsidize car driving with their tax dollars.
Americans like cars so much because they're incredibly useful. And public transit sucks, which is sort of a chicken-and-egg problem. We don't want to invest in something which is unpleasant to use, so it remains unpleasant to use. In my city, we have the additional problem that the local transit agency only wants to spend money on light rail, which is just a smaller version of the "nobody builds subways to subdivisions" problem. I'd be more likely to use mass transit if the bus was clean, comfortable, and came a lot more often than once an hour.
Yeah, I always describe it as the US setup being in a relatively stable configuration currently and the mass transit solution being another very stable setup but the transition between the two being both painful, expensive, and time consuming.
It isn't so much the spread out, as that there are not good routes for mass transit in most suburbs. Transit needs long straight lines with destinations along them. When roads wind, and destinations are at the end of cul-de-sacs transit has not chance because riders are forced to spend a lot of time making no progress in the actual direction of their destination.
But even in built-up cities, Americans cling to their cars just like they cling to guns and religion. Look at all the uproar in Manhattan, NYC, where they're taking away street parking and putting in protected cycling lanes. People are upset at this "attack" on cars, and somehow think they deserve free places to put their personal vehicles. If you look at another highly built-up city for comparison, Tokyo, they don't have this problem. There is NO street parking; it's all paid lots that cost a fortune. In fact, you're not even allowed to buy a car there unless you can prove you have a place to park it! So most people get around with subways, trains, walking, cycling, and taxis.
The bottom line is that it's cultural: Americans just don't like public transit and don't want to fund it with their tax dollars, but they do want to subsidize car driving with their tax dollars.