AFAIK, the ventilation systems are only convoluted in the sense that they use a heat exchanger to minimize the temperature difference with the incoming fresh air. It’s not a hack or afterthought: The idea is that airflow is very important, but it needs to be controlled to maximize energy efficiency.
Relying on passive ventilation that wasn't designed as such is also not a good way to achieve removal of these nasties. You can see that if you open a window when you have high CO2 - it doesn't drop at any speed.
Relying is the important point. Sure, it may be fine, but it often isn't, and probably is uncomfortable in winter. And that's before we get to energy losses.
