First off, the big problem with diesel is not CO2, but NOx gases, which are way more immediately dangerous to human health. That's why some
cities are thinking of banning them ASAP right now.
Second, besides VW which was creating even 40x the emissions than the standard you mentioned required, pretty much all the other car makers were creating 10-15x as many emissions, too, thus making that "strict standard" way looser. Forget Euro 6 or Euro 5. These cars weren't even compliant with the 25 year old Euro 2. In other words, all of these car makers "passing" the emissions tests over the past two decades has been all a bad joke played on the EU population.
https://www.theguardian.com/technology/2016/sep/19/many-car-...
Finally, a new stricter (than Euro 6) standard was supposed to arrive by 2021 or so, but Merkel once again intervened to make the standard even looser (by +50% more emissions allowed) than the previous one, which would be a first in the history of the Euro emissions standards, which have become increasingly stricter not looser, so far. All thanks to Merkel.
https://www.theguardian.com/environment/2016/oct/24/petrol-c...
https://www.theguardian.com/environment/2013/jun/28/angela-m...