Peacock is the national bird of India. Peacocks symbolize ego and pride. In Indian Mythology, Lord Krishna dons a Peacock feather on his crown. While I don’t know the reasons, maybe this link can help. Needless to say I find this practice of selling peacock feathers inhuman, but I know that the stunning bird sheds its feathers every year. Till it is not killed for aesthetic beauty, I guess its fine.