Because man has messed with their genetics to the point that the animals cannot see well enough to live a normal life. They are the most likely by far to be taken by predators because is this.Curious why you feel that way about polish? Never had them btw. But I do keep silkies so can't say I agree there....lol. curious minds...though
Additionally, when lone specimens are kept with properly feathered birds they are very frequently attacked due to their odd feathering.