Because Christianity is hard. It demands personal responsibility, thought, sacrifice, hard work, dedication, and faith.
Witchcraft and astrology are for lazy people. It's bogus, make-up-as-you-go, something-for-nothing, tailored for snowflakes who have been told all their lives they are special while accomplishing nothing.
They probably know nothing about Christianity. Do you really think most of them went to church or Sunday school?