Because it symbolizes the essence of life, and to see it drawn is the end of said life.
Besides that, I think it’s in our system to generally be repulsed and grossed out by blood as motivation to stop the flow when we get hurt. I think it’s a survival thing.
I mean if you find a corpse or a skeleton in the woods, most peeps would be afraid…but why? It’s not like it’s gonna get up and kill you. And yet…
I find blood intriguing myself, it looks pretty and romantic kinda, but only when pictured on something dramatic, like some Goth poem with a picture of a rose dripping with blood on it, or seeing fresh blood make funny shapes on the floor.
But massive amounts of blood is pretty gross, especially when it comes from a dead body, and it also smells really bad, so that doesn’t help much.