In the past there was always an open and frank exchange of information that would be given freely for the benefit of safety
The nature of aviation accidents often means there is no one left to have a "frank exchange of information" with. In this particular case, as many have noted, it's reasonable to expect that the pilot would not be able to recall precisely what happened due to the severity of his injuries and the amount of time that passed before he could be interviewed.
Speaking generally, I don't think there was ever a time in history when people weren't self-serving and motivated to cover up reckless acts. It would be very rare to have someone say "Yeah, I thought it would be fun to [commit reckless act]."
Fortunately, in modern times we have an amazing ability to analyze wreckage and we often have access to recorded data that precisely reveals what happened. That sort of evidence doesn't involve relying on "frank exchanges". In this case there are numerous video recordings that show in great detail what happened. Video recorders aren't going to start lying or refuse to cooperate if they are used in the police investigation.
Speaking generally again, in cases where there has been a "conscious, substantial and unjustifiable disregard for risk", how to you prevent future occurrences? I think the threat of prosecution is going to do a lot more than an AAIB report.
It's certainly gotten the attention of a lot of self-described display pilots on PPrune, and I think that's a good thing.