The appeal is that all your decisions matter more and your mistakes hurt. What is crazy in this instance is that those mistakes cost you 50+ h of your life.
HC in these games are mostly for non lifers even when some of them will not admit it.
Perhaps, but otoh, if I've played the same build for 50h, I'm likely getting bored of it.
I tried to play standard once (first league when they switched to 10 acts). It was awful, and I quit in act 6. There was no tension in it, just the inevitable grind to victory.
I like HC because it means automatically getting a large variety in my builds and a lot of tension. In HC, losing 60% of your health feels exciting, in standard I barely cared when I dropped to 10%.