My understanding is that the safest position in a car accident is the centre of the rear seats. For example this paper finds that 0-to-3 year old "children seated in the center rear have a 43% lower risk of injury compared with children in a rear outboard position."
I have been looking at seat layout for some potential car purchases and it seems universal that ISOFIX mounting points are available for the outboard positions only. I have looked at Volvo XC90, Ford Grand C-Max, VW Passat and Vauxhall Meriva.
Why is this? It seems to me that ISOFIX mountings are little loops of metal attached to the body of the car, the best picture I can find online is this answer. Adding an extra couple of these loops to the design of a car seems like it would add little to the overall cost or weight of a car. Being able to offer a 43% lower injury rate to customers with only one child, or who frequently only transport one child, would seem a big selling point. Governments put in lots of regulations concerning this, they could legislate to require it. Many customers, myself included, would be benefit from such an option. Given that it seems in everyone best interest, why do cars not have mounting points for a single ISOFIX child car seat in the centre?