Ask for help…

Last week I rescued Christophe Thibaut in a mail. He was actually glad about the result. ( I proposed to use the 5 Why’s and the 9 boxes in an answer on a checkin of him.)
He replied with this general ask for help:
Ask for help : If you have some piece of advice in mind, [...]

What would I need the five Why’s of the Toyota Way for?

I did not follow the Toyota way session at XPday London [Sorry Pascal], so I did not have an answer to my trouble with the five why`s. My question is, what is so good about the five why`s in lean?
As a coach I prefer using specific questions like:
Who
What
How many
When
And not why.
Why is the question my [...]