reason = something that provides an explanation
cause = agent that produces an effect.
They are highly synonymous terms
What was the reason for the traffic jam? ok
The reason for the traffic jam was (that there was a bottleneck). The bracketed noun clause is something that provides the explanation.
What was the cause of the traffic jam?(O)
The cause of the traffic jam was a bottleneck. Bottleneck is the agent that brought about the chaos on the roads.
This is my understanding.
Student or Learner