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.

Huh for me it drops down to 400 within minutes when I open a window

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.

I guess you and the person before might have different circumstances in how your windows and rooms are set out, local prevailing wind and so on.

I have to open two windows in my home office, otherwise the co2 just hangs around.