The English words for use in questions don't have much to do with the range of things we ask. This set is conveniently mnemonic, but it is not otherwise special.
It could be smaller: We know, for instance that spacetime is unitary -- 'when' might just as well be 'where'. And even before physics got that far, it has been so in other languages, which have an 'at' that applies to both space and time and basically ask 'at which'.
It drops whole categories of questions, for which we then invent odd idioms. "How many/much/long?" translating 'Quando?' has nothing to do with any other meaning of "How?".
It also already conflates important distinctions: We know that 'Why?' means at least four very different things, as it can capture any of the types of causes pointed out by Aristotle: "Through what process?", "Unto what end?", "On account of what prior circumstances?", and "Because of what concurrent facts?".
And its divisions are not clear. For three of those meanings of 'Why?', we also use "How?" making a total hash out of propositions like "Science prefers 'how?' questions to 'why?'questions." (There is content to the assertion, but it is not logically connected to questions that can really be asked with those pronouns, since those overlap broadly.)
This is a case where we use ambiguity and incompleteness to our advantage. We know that questions are seldom complete and need to be analyzed. The poor tools generally do not get in the way of far more complex meanings than one would expect.
You can tell by the forms in most of Latin, that it started out with one basic root for most indefinite constructions: 'quo'. With a few major exceptions like 'ubi' everything is timeworn abbreviation of some general sentence construction with a form of 'quo' used as an algebraic variable. "Quo modo?", "Quoque?", "Cui bono?", 'Quisnam?"... Starting from a very small fund of question words does not seem to have gotten in the way.