An approach to understanding the end of the magical era of the Old Testament:
Today scientific rationalism and materialism may be causing people to automatically filter out the supernatural around them, whether of divine or demonic origin.
Also, regarding why we may not be seeing more divine signs and wonders in our day, we read of divine miracles in the New Testament being used to validate (Mark 16:20, Heb. 2:4) the true gospel of grace (Acts 20:24). But I would argue that today’s message is watered down with religious legalism and rationalism, a gospel which God will not confirm with signs and wonders (Gal. 1:6).
But, as a futurist, I believe even the skeptics will be convinced of the supernatural nature of coming false signs and wonders (2 Thes. 2:9-10), just as people were amazed by the undeniable activities of Simon the Sorcerer in Acts 8:9-11.