You can still die from carbon dioxide exposure/oxygen inefficiency. It will just take longer, now that carbon monoxide emissions are down because of catalytic converters eliminating a lot of them. And yet, a lot of people still die or get seriously injured, particularly because their "keyless" crap acts up [1].
I agree that carbon dioxide exposure is dangerous, but it is probably less dangerous because (TIL) there's a specific brain mechanism that wakes you up when your blood has elevated CO2[0].
On the other hand, carbon monoxide poisoning will only wake you up if its symptoms (among which headache, nausea/vomiting, elevated heart rate, and cardiac arrest seem likely) do so.
[1] https://www.nytimes.com/2018/05/13/business/deadly-convenien...