The princess doesn't want a gem on her finger that has been cultivated by a nerd and comes with a "vegan, soy-based, cruelty free" approval on it. She wants a warlord to return from conquering and pillaging foreign lands, leaving rivers of blood in his wake, to deliver the prize to his queen as a symbol of her value and his material investment and dedication to her.

Obviously no woman in her right mind is consciously thinking that, but that's the psychology behind it. "Bloodless" is icky.