Because Satan is their master and he is as scripture tells us, the father of lies. This is in direct oppostion to the Word of God. I do not condone nor agree with this use. The power behind all kinds of witchcraft is Satan. He is the author of all deception, and all rebellion.
Witchcraft leads to an eternity in the lake of fire.
Open your Bible. It's all there in black and white. The Bible clearly condemns and warns against the views and practices of witches and witchcraft. Witches can believe what they want, but they should not delude themselves or others with the notion that their views square with the Bible, the church, or Jesus Christ. Witches should not distort the teachings of the Bible or Christianity or tamper with the teachings of Christ to fit their false beliefs and practices.