For why (also hyphenated or written as one word) meaning why as a direct interrogative was used in old and middle english (see the med's entry), but it became obsolete. There are also many examples of why we cannot, but they are not interrogatives You never know, which is why.
Why Text Question · Free image on Pixabay
And goes on to explain
There is a subtle but important difference between the use of that and which in a sentence, and it has.
Why is [etc.] is a question form in english Why is the sky blue Why is it that children require so much attention Why is it [or some thing] like that
When used in as to why, how whether etc., it is often better to drop as to and simply use why, how, whether For example, i don't understand as to why you are going there I don't know as to. As to why present day usage is as it is
See also why does zzz mean sleep
The reason zzz came into being is that the comic strip artists just couldn’t represent sleeping with much
