I believe 왜냐하면 comes from 왜냐고 하면, which literally means "if you were to ask 'why'". 왜냐하면 = 왜 + 냐고 하다 + 면 as you know, 왜 means "why" 냐고 하다 is an indirect quotation of a question. In this case, "why" is the one being quoted 면 means "if" in this case The 고 in 냐고 하다 can be omitted, so you often see it as 왜냐하면. You might also see it written as 왜냐면, I think it's due to 냐 + 하 stringing together when you say it, so it sounds likes 왜냐면. Plus, it's already known that the grammar pattern is 냐고 하다, so 냐 by itself can already be understood :).

- 냐 - is the interrogative suffix 왜냐하면 as far as i know is , "if you want to know why~ " kind of thing.

The word "왜냐하면" is an conjunctive adverb, literally meaning "if it were asked (by someone) of why it is so". "왜냐하면" is contraction form of the word"왜 그러냐 하면", or "왜 그런가 하면", and it can be again contracted to "왜냐면". As far as I know, there is also similar expressions In English, like this. For examples, "if (it is) so", "if (it is) possible", etc. And Its function is similar to the function of the conjunctive adverbs in English, such as "hence", but its meaning is a little bit different from "hence".