Because I would have done something others had not done. The doctrine of predestination more than any other teaching of scripture takes salvation out of man's hands and places it in God's control. Men do not like God's control. The cause of God's choosing or predestination is found in Him. If we insist that we played a part in God's choice, then human merit is brought into the picture.
Salvation then becomes synergistic rather than monergistic.
Biblical salvation is monergistic. Christ alone, by his complete and finished work saved me. Within a synergistic scheme, salvation becomes a cooperative effort. My work takes away from the work of Christ. I made a contribution.