Because the basic, universally understood word has gotten us as far as it can. Change it, and we get somewhere else. The definition does not have to be exhaustive to be useful.
Far from it. It would teach me a new definition of a word, and why you use it that way. Confusing, yes. Unnecessarily, not at all. In fact, confusion is necessary to learn.
You are saying the same thing, and expecting me to change my answer. Saying that belief is this, because 99.9% of the English speaking world says it is, doesn't make it so.
You are logically correct. But your premise is incorrect...so it doesn't really matter.