That's not strictly true. Not everyone is in it for the investment. There's many of people who do what they can in Bitcoin and then convert their Bitcoin into fiat when they need to pay bills etc.
I don't think Bitcoin will become a national currency per say, at least not for a very long time. It's currently making some waves but, in no way is it currently competing with traditional currencies. Even though it's conversion rate is the biggest it's been. For Bitcoin to become the main stream currency in a country and considered the national currency would require several big movements/organisations/companies to start trading in Bitcoin.