The average person isn't smart enough to understand what a stock market is, how it works and how to buy/sell stocks, either. That doesn't mean they're not used.
The reason they are used is that there is an entire abstraction layer around it, all you have to do is give your money to the guy whose face is on the billboard. As a crypto currency, bitcoin is fundamentally incompatible with this model.
There's nothing to prevent that level of abstraction being built around bitcoin. The average credit card user doesn't understand what's going on in the background, just that money from their bill is transferred to the merchant.
