The reason I think it's mostly speculation and fraud is that the only people I know who have crypto currency in real life have it as a speculative investment and that combined with the fact that it doesn't work well as a payment processor (historically it's been slow and expensive and even mainstream companies that used to take it seem to have often discontinued support). I actually don't think they are mostly fraud, I think they are mostly speculation and fraud is just the outcome ofof a speculative market with little regulation. I would be happy to hear about more use cases but most I've heard about have either been small toy use cases or "in the works".