Can't compare the ladder charts like that since so many more people play soft core that the comparison becomes irrelevant.
People just don't like to play slow or over prepare like you should in hardcore. They prefer soft core in most cases because they don't want have to restart entirely in the event of accidental fuck-ups or uncontrollable lag on server side, etc.
My guess is that once (if?) a shared stash is implemented so that making is easier and people can move arcane crystals and things that make early game grinding in hardcore extremely slow, more people will play HC without as much rage when they die since they'll already have a bit of a head start on a new character.