People are still buying lots of mini suvs with $3-$4 gas, so I'm not sure the blame lies solely at the feet of the auto companies.
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.
Most car seats these days take up more room than a full sized adult in the same spot.
There is no reason a small child needs an oversized seat. Crash protection is not about the amount of fluffy foam surrounding the child.
Plenty of families could do with a smaller car if appropriately sized seats could be made available. It is physically impossible to fit 3 child seats into a medium sized car with 3 seating positions.
Those wondering why leg room is constrained by a child seat, which, presumably, needs no leg room, haven't looked at the design of a child seat. These raise the child up, and with the backward rake of the driver seat, the front of the child seat rests against the top of the backrest of the drivers seat, leaving no room for the childs legs and feet.
The problem is even worse in the case of a rear-facing baby capsule. It would be easier to load a 60 pound dog into the back seat of a car than a child capsule.
Ironically carmakers themselves have designed small and efficient child seats that integrate with their cars to maintain interior space whilst providing maximum protection to the child occupants. But because of byzantine laws in each international jurisdiction where vehicles are sold, few of these can actually be sold, meaning the cost is high if they are available at all.
It's a case of poorly thought out regulation and an obvious marketing ploy of 'bigger is better' for parents when purchasing a seat for their most precious cargo. Because when it comes to persuasive arguments 'won't someone think of the children' trumps all.
Three years ago, the guidance was to keep the infant car seat rear facing until age 1. Then it became until the child reaches 20 lbs. Now the guidance is to push to age 2 with the additional recommendations to go even longer if possible.
I believe that the proliferation of side impact rear airbags has forced the safety guidelines in this direction. Side impact rear airbags are a great safety feature for adults, but they can be fatal to small children. A car seat is the only real defense you have against them. And the manufacturers aren't taking chances with letting the airbags be disabled based on weight requirements.
Nobody likes to take chances with their kids, but we've also gone a little nuts with safety in the US, using "bigger is better" to handle every safety issue and with all sides so worried about getting sued that we've created this unsustainable escalation of safety features in cars.
This has the net effect of keeping us in larger cars for longer and preying on our emotions to keep us from switching to more practically sized vehicles. As a parent who tries to make practical and rational decisions, I find it really frustrating.