It's not that easy. Sure, what they done can be considered "evil"... but what if they had refused to do it? They would have most likely lost their jobs and they would have no chance in a court trial. Volkswagen has a army of lawyers and is in tightly connected with every relevant government agency in Germany.
The problem here is Uncle Bob thinks he's in the trenches when in fact he's armchair quarterbacking.
But the other possibility would be to "blow the whistle" anonymously.
The chances of getting away with that still aren't great (if VW put some effort into flushing out the snitch, I think only a practised liar could get through it...), but it's another way forward.
And actually: it's possible this actually happened, and the official story of how this was discovered is just a cover for an anonymous engineer who managed to get a warning to the right person.