HC comes with it's own built in end game, exclusive to that mode. Death. ...or....avoiding death. Permanent death. Your character isn't rolling over to SC like in PoE, this is real HC.
HC has rewarded me endlessly. It saved D3 for me when the game was at it's lowest points early on. Now that D3 is a legit top-shelf ARPG (IMO), I am bound to HC mode. I simply couldn't enjoy the game without it.
Objectively speaking; HC adds an aspect to the game that it currently doesn't have outside of HC. It makes it possible for you to lose. It's a game, you should be able to lose. There is no PvP, so if you want to risk loss, hardcore is for you.