> dramatic oversimplification
> single answer
If someone pitched it to you that way, I agree that's a dramatic oversimplification -- not of causality, but of what's meant by the "Five Why's."
"Five Why's" is a tool, a reminder to separate the symptoms from <waving hands> whatever complex system dynamics that caused them. Nothing about that analysis has to be linear nor yield a single answer.
The key lesson is to never solve a problem on the same level it was created -- i.e., the symptoms. Take the time to think through the causality. If you can go five levels up/away from the symptoms and still find an actionable mitigation for a whole class of problems, great! More likely, you go up one level and at least you won't experience the exact same symptom twice.