Basically 'cause of some nonsense with bloodlines, you get people who think their blood is somehow inherently ~superior~ [ YOU CAN HEAR THE SARCASM, it's practically dripping off the word. ] above us common folk. Something about how certain things and qualities are in the blood, or some other bullshit. Then they set up some system with them on the top. That's 'nobility'.

Venus grew up being part of that group, and she was probably told about how she's just better than everyone, so of course she's gonna think she is.