Why do we need question marks

Aren't they a redundant form of punctuation. Put aside the fact that you are used to them. Do you need them. We don't often use them when we write on messenger apps. Questions are obviously questions. Sometimes statements seem like questions. This is a version of the rhetorical question, like the first sentence of this blog. Why favour the question mark: the ambiguity you actually want from the statement is better achieved without it.