The reason music with a simple recurring rhythm exerts a strong primordial appeal is that it reminds us of the womb environment.
Premise
The first sound heard within the womb is the comforting sound of the mother’s regular heartbeat.
Intermediate Conclusion (so)
In taking away from us the warmth and security of the womb, birth also takes away a primal and constant source of comfort.
Intermediate Conclusion (thus)
It is extremely natural that in seeking sensations of warmth and security throughout life, people would be strongly drawn toward simple recurring rhythmic sounds.
Main Conclusion
The reason music with a simple recurring rhythm exerts a strong primordial appeal is that it reminds us of the womb environment.