Do we know for certain that exploitation or rule breaking has occurred here. It seems that everything said on this so far is pure conjecture. He might have had a CPL if he was doing regular para dropping. It is entirely possible that this was a properly conducted commercial flight. It is also possible it was a legally conducted private flight. It is possible that he was not that familiar with flying this particular aircraft in IMC conditions, and he could have become overwhelmed with icing in an unfamiliar aircraft, but we don't know anything for certain other than the aircraft is missing. He could have had a heart attack for all we know, or the passenger may have had a panic attack and distracted the pilot. This is all pure speculation of course, like everything else mentioned here so far.
All the people suggesting tighter regulation might want to be certain of what, if any, regulations had been broken here, and how tightening them up would have changed things. I do not believe that regulations, broken or otherwise, have contributed to the unfortunate outcome. There are plenty of aircraft piloted by two commercial pilots on properly chartered flights that have also ended tragically, and also Commercial Air Transport journeys don't have s 100% success rate.