Cars are getting extremely air-tight and ventilation is an important factor for safety and health. Outdoor fresh air can be measured by the amount of CO2 which today is around 400ppm in rural areas. In a building a standard of maximum 1000 ppm is tolerated. You can feel when it exceeds that level in a full meeting room, you start to yawn, and that is a silent scream for fresh air.
A car with activated recirculation can easily reach above 4000ppm within 15 minutes. Meaning that the cabin air quality becomes a danger since it reduces our cognitive abilities and reactions.