I'd like to add at least one issue to the 'reasons why'.
Not enough enroute weather reporting - weather reporting is for fixed wing, it seems. Many facilities don't report weather after normal working hours, the facilities are widely spread out and don't consider the problem areas like mountain passes.
Some major cities have no ATC after midnight. And a lot of the time you're operating at such low altitudes that you can't talk to anybody.
Also, no good helicopter appropriate instrument procedures to get us into hospitals and the like.
And not enough performance! At least one recent helicopter crash appears to be caused by operating way outside the capabilties of the machine, and I know we have to keep reduced fuel loads because of the hot and high performance (or lack thereof).
There, I've got that off my chest.