If IIMC accidents were primarily confined to PPLs, then I would believe that poor decision making/captaincy was a primary underlying cause. However, it seems that IIMC misadventures are well distributed across the experience range. It also seems just too frequent to blame on poor decision making.
Maybe weather conditions in many flying areas are just normally unpredictable enough that flying un-stabilized, un-autopiloted helicopters is just inherently dangerous.