Diesels were essentially mid-sold to people for whom they were unsuitable. They were sold on better fuel economy and grunty torque but are not great for short journeys.
People also started panicking when they encountered an active regen, with the car driving a little differently and smelling hot and the fans running on after shut down, because nobody explained them.
Passive regens usually happen naturally with no action needed, but do require certain speed and revs to trigger. Aunt Mable would rarely trigger these regens on the 2 mile round trip to the post office.
And then as the DPF filled up it would trigger more and more active regens which would drive fuel dilution into the oil which wouldn’t evaporate because the engine never got properly warm and so round and round we go in a self-destructive cycle.
When VW got caught with the whole cheat device business I had a Škoda Yeti with an affected engine. They tried to get me to have the official remap update and I refused because I knew it would lead to problems. Sure enough, after updates there were plenty of reports of failed EGR and DPF systems.