God does not bless arbitrarily but normally uses means to bring about His desired ends. Assuming that spanking is unnecessary.
Many parents are guilty of false tenderheartedness.
God has said that the rod is essential for biblical training. To withhold the rod is to withhold one of the ordained means of wisdom and salvation. Assuming that spanking is all that is needed. There are parents who think their sole job in regard to child-rearing is to spank their children. Assuming that what is obvious to you is obvious to them.