The causes are well known....
Night flying in unlit areas without NVG's....
Night flying without adequate surface light reference to control the aircraft.
Lack of weather reporting along the route.
Taking off at minimum weather conditions for VFR flight....to encounter deterioating weather conditions.
Striking unlit obstacles at night during scene operations.
CFIT in IMC flight.
Equipment/mechanical failures.
Chopper Shopping by Emergency Dispatch Centers.
I would suggest "commerical pressue" is less an issue than "personal....self inflicted pressure" being a culprit.
One recent case involving Omniflight Helicopters in a fatal crash in South Dakota.....involving a Japanese Pilot seems the most interesting one to study. That is being done in civil court as we speak I think.
EMS pay is embarassing.....the use of " no-notice-hurry up and get airborne SPIFR flights " are like rolling dice in my view....as are hurry up and launch night flights either VFR or IFR when marginal weather exists.
FAA Part 135 has a requirement for adequate surface lighting to control the aircraft for night VFR flight....but in the industry....ignoring that is commonplace. As a result....there are lots of IIMC occurrences....some of which result in crashes and fatalities.
One man's opinions here......