Why do helicopters crash in low visibility (IMC)?
The only flight rule that will completely eliminate human error is to ban people from flying planes or programming UAVs.

More regulations won't solve this.  Aviation is already strictly regulated.

As for why the pilot did not climb, well, you will have to ask him.

Keep in mind that a mechanical failure could be to blame.

We just don't know.

Answer to the previous question:
The risks of continued visual flight into poor conditions are already pretty well documented.  It is a serious hazard for all flying machines, not just helicopters.  We don't know if that is what caused the crash or is even a contributing factor, though some of the makings of a CFIT accident are present (bad weather, possible perceived pressure to go, and possible complacency due to familiarity with the area).  Anything we say here, including what I just typed, is pure speculation.

We don't know why the helicopter crashed and we will likely never know for sure.  It was not equipped wIth a CVR or FDR nor was it required to be so equipped.

This is a tragic accident and that's all we know.