Way better than eating cans of dog food in Mad Max <I can't, so I just don't play that game>

And really we are zombies anyway so eating other undead body parts for food makes about as much sense.

And leeches probably get blood from other things they eat like boar / fish whatever ends up in the water... Don't think drauger even have blood since they are undead? The greydwarves probably don't either seeing as they are Ent children....