I see Jung's idea of synchronicity in the meaningful coincidences. As for the increasing number, well, the number of events in everyday life is much greater than it was for previous generations. I do agree that we've hit a point at which the pace of development is increasing, but I view this is related to the increased availability of information.
This also contributes to the popularity of the book. In every age, there has been a desire to hear that great events are coming to pass now.
Consider what coincidences are: connections that our worldview interprets as meaningless. If you are going to claim that our current worldview is somehow incomplete, then the obvious place to look for supporting evidence is to find meaning in these connections.
Some of the coincidences in the book are better described as communications from the unconscious. Ever since Freud, psychologists have recognized that stray thoughts, daydreams, and memories are not really random.