Here’s a better theory: because American public transit is, when compared with the alternatives, not safe, not clean, and not convenient. Take LA, probably the most car-dependent big city in America. Riding the bus or subway in LA is not an enjoyable experience. Nor is it enjoyable to walk around the areas where the stops are. If I were trying to get more people to use public transit, I’d start by making the stations and buses/subways beautiful, clean, safe places that are just nice urban places to hang out in. There’s no need to make it a moral crusade; just offer a better product and more people will use it.
Part of this is a structural issue. The Federal government has a robust system of funding road network expansion but has no equivalent system of funding transit. Even after the passage of the recent infrastructure bill, look at the apportionment to maintaining Federal roadway compared to Federal transit funding. You can't compare a budget Android phone for a developing market with a flagship Android or a new iPhone.