It's like this, games and especially the ones violent or gory ones have to make you feel like a god, feared, etc. They do this by having your actions (the cause) damage the opponent/cheese/monster (the effect). In reality, if you take an axe and slam it into soft fleshy bodies you would see blood and guts, so the games try to replicate that and have zombies dropping bucketloads of blood. If you didn't see anything happen, then it feels like if you didn't do anything; hence making you feel weak and not like an all powerful deity.