Sorry I had to do a button

Hmm... What if those Ordinary people are as they are because they can't be altered?

The reason could be Mystical, Physical or even Mandated by the existing governing council

Mystical reasons could be something nebulous like the world spirit prevents a certain percentage of humanity from being changed, this could also keep Ordinaries from being killed for sport because it disrupts the flow of the supernatural energy.

Physical reasons could range through Rare blood types that are either too tasty to lose or critical in some way
Example: Rare Blood type = The blood of this person is so powerful that any Vampire holding one in their herd guards them like gold
Example: Rare Genetics = This type is illegal to change from Human to Vamp, Ware or other type because they become a true monster of this world killing the Supernatural types (of course once this type is converted they become a GM only NPC)