The issue in this case is that, over water and under overcast - it is possible/probable that there was zero exterior reference. Thus, whilst legally VMC, of no useful purpose.
This.
The regulations have a well known gap when it comes to night flying; It is possible (and certain over long stretches of water) that in night VMC conditions, there will be little or no visual reference from the surface. Arguably, the requirement for VFR flight to maintain visual contact with the surface would be hard to prove sometimes - yeah, I know it's down there, but I can't actually see it. Is that actually flight in VMC? Not really.
Let alone the poor weather conditions associated with this accident, the flight would still have been challenged even on a clear night. JFK Jr. had an accident in very clear conditions over water at night as a result of loss of situational awareness. There was "get there itis" involved, and low experience in a well capable airplane. Only pilot decision making improvements will make this better. In the mean time, eagerness to provide a VFR transportation service in other than clear day conditions should be viewed with great skepticism.