Well its not as though those taking pnaps would tell their hc
By the time hc do realise, the kind of people who take pnaps are the same ones who have the highest scores usually, so I can see why they can be difficult to kick from an alliance. Due to not caring about their current alliance (face it, you dont if you have a pnap to an enemy ally/block), they would just roid the ally they got kicked from :P