Yes, I agree, Buddha's exposition on rebirth is not trivial. There are actually a lot of other supporting concepts to learn first in order to make sense of that.but in essence, he taught all these because he saw that human beings suffer in life because of specific causes, and wanted to help them in their journey of being liberated from their suffering. His primary role is a teacher (a very wise and enlightened one).
Human beings suffering could also be a test. To Muslims this is a temporary world. YOLO. Dont be surprised if you hear some muslims praise God even misfortunes befalled on them. To them is a test of faith.

