Why do people turn to astrology, witchcraft and the like?

One thing we must understand is that all humanity is totally depraved (sin that effects every single part of us) through the fall of Adam. His nature was physically changed thus, why we read in Genesis 3:

GEN. 3:6 When the woman saw that the tree was good for food, and that it was a delight to the eyes, and that the tree was desirable to make one wise, she took some of its fruit and ate; and she also gave some to her husband with her, and he ate.
GEN. 3:7 Then the eyes of both of them were opened, and they knew that they were naked; and they sewed fig leaves together and made themselves waist coverings.

Therefore, everyone born hereafter inherits a fallen nature which Pastor Armstrong explains as being a "spiritual birth-defect." Adam's perfect nature was forever changed.

ROM. 5:12 Therefore, just as through one man sin entered into the world, and death through sin, and so death spread to all mankind, because all sinned—

With the understanding that all humanity has total depravity, we are now able to reconcile why people pursue worship (or partaking in) of created things over the Creator, we can simply turn our attention to God's Word

ROM. 1:18 For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of people who suppress the truth in unrighteousness,
ROM. 1:19 because that which is known about God is evident within them; for God made it evident to them.
ROM. 1:20 For since the creation of the world His invisible attributes, that is, His eternal power and divine nature, have been clearly perceived, being understood by what has been made, so that they are without excuse.
ROM. 1:21 For even though they knew God, they did not honor Him as God or give thanks, but they became futile in their reasonings, and their senseless hearts were darkened.
ROM. 1:22 Claiming to be wise, they became fools, 23 and they exchanged the glory of the incorruptible God for an image in the form of corruptible mankind, of birds, four-footed animals, and crawling creatures.

ROM. 1:24 Therefore God gave them up to vile impurity in the lusts of their hearts, so that their bodies would be dishonored among them.
ROM. 1:25 For they exchanged the truth of God for falsehood, and worshiped and served the creature rather than the Creator, who is blessed forever. Amen.
ROM 1:26 For this reason God gave them over to degrading passions; for their women exchanged natural relations for that which is contrary to nature,
ROM. 1:27 and likewise the men, too, abandoned natural relations with women and burned in their desire toward one another, males with males committing shameful acts and receiving in their own persons the due penalty of their error.
ROM 1:28 And just as they did not see fit to acknowledge God, God gave them up to a depraved mind, to do those things that are not proper,
ROM. 1:29 people having been filled with all unrighteousness, wickedness, greed, and evil; full of envy, murder, strife, deceit, and malice; they are gossips,
ROM. 1:30 slanderers, haters of God, insolent, arrogant, boastful, inventors of evil, disobedient to parents,
ROM. 1:31 without understanding, untrustworthy, unfeeling, and unmerciful; 32 and although they know the ordinance of God, that those who practice such things are worthy of death, they not only do the same, but also approve of those who practice them.

Nevertheless, because of the fallen nature inherited, mankind on its own will inevitably turn towards selfish desires and worship things created as we read in Romans, if and not until God initiates salvation within someone, being born-again into the bloodline of Christ.

We strongly suggest an in-depth study of Romans to fully grasp these verses for your studies.