It might have been less expensive to get a new car seat ?
In the US people have bigger cars (in general). Parents seem to want to maximise the size of the seat. As a result, it's my hypothesis that small sized car seats do not sell well.
The flow-on from this is that it probably would be very difficult to purchase two car seats that would fit comfortably into a small vehicle, like a VW Polo or similar.
In addition, there are other factors that drive the choice of a larger car, including space for the various other things that babies come with, like prams. And most people prefer larger than smaller when choosing a vehicle. People in Europe choose smaller cars for a variety of reasons, including parking, fuel costs and road size.