Well, I think part of the reason is something said in this article:

"It really has the potential to become the native unit of exchange on the internet, But that won’t be possible while it’s being inflated by traders who see its value mainly as speculative investment."

I'm not exactly sure it will fail, but an unit of exchange with such high volatility is complicated as a currency, isn't it? Seems great for high-risk, high-gain investment, but the de facto currency of the web? I'm not so sure.

Also, what I know about economy I learned from the interwebs, so feel free to correct me if I'm talking bullshit :P.