well for one thing, simple negligence is not criminal negligence. Fraud is criminal, so it is intentionally harder to prove. and i think don't criminal negligence really applies here, but if so would have an equally high bar.

what happened also seems to fall much more squarely under fraud (e.g. lying to the FAA) than simple negligence. failing to notice that they missed steps or didn't complete paperwork would be negligent (which they probably have done), but existing criminal case is about intentionally lying about a design change and it's ramifications to game the certification process. that's really bad. way worse.