Why is it that...?

I don't think that Hume intends that the argument can be settled for sure (if that is even possible, when one can qualify any possibility into existence, therefore dodging inconvenient tests and criticisms) all he suggests is that one compares a state of evidence against the absence of it and, upon that, form an idea of likelihood. We don't treat every claim the same in life, we use reason to decide between them. I don't think that is an unsound path to proceed down. If Hume is guilty of assuming that miracles exist because there is no evidence, then supporters of the notion are just as guilty for assuming they do for the same reasons.