Well corporations were put together for this exact purpose, to protect individuals from legislation. A corporation can pay it's board members millions in salaries and bonuses, then have no assets and declare bankruptcy and not pay creditors. The creditors can't come after the individuals for the money cus the legal entity that owes them is the corporation. Same deal with criminal charges, unless you have a prosecutor willing to go after the individuals and show criminal intent. I'm no lawyer, but I think it's a hard case to make. The corporate entity protects their incompetence and it's hard to prove willful criminal intent over just sheer stupidity. When it's a whole entity it's hard to blame individuals cus everyone is a little guilty, who is the most guilty and deserves jail time? I do agree in both cases there should be jail time for the managers who made the decisions, and the rank and file engineers should be investigated to see if they willfully did this or were pressured to do it to keep their jobs. If it's the latter I wouldn't blame them, but blame the management.
The GM thing is even more dubious cus the US government had bought a ton of shares in them as part of a bailout in 2009, and sold their stakes in late 2013 I believe. So only a year before this story broke the US owned a huge stake in GM. I feel like that conflict of interest drove some of their light penalties cus they wanted to save face. The bailout was already unpopular with many on the right.