Don't only think Bitcoin for investment. It's much more than that, people use it for different purposes like for transfering money, payments, investing like in share market to earn profit etc.
Bitcoin not only for investment. Its a fully distributed systems that exhibit a principle of TRUST without the central of authority, without a third party between all the transactions, its a digital currency. It's easier to use and useful especially in remote places that don't have an access to bank. You can use bitcoin without using dollars, less expensively than the visa network or safely in line with trade.