I apologize in advance, but this feels rather un-German...
What was the motivating factor in this? This blowout is going to affect so many of VW's lines, and their reputation.
The new ones really drive with pep, like normal cars, so I think they thought they'd sell more with better performance. There is a not insignificant price premium for diesel vehicles.
Diesel owners are really really passionate about their cars (no time to redesign their web forums) and "Diesel Gate" is going to hit that loyalty hard.
Summary page with graphs: