I think the price volatility, lots of incidents related to black market activities and many other anti-government activities are the major cause that's stopping people from using bitcoins.
I don't think BTC price volatility is the primary cause for not using it. But based on my knowledge as of now bitcoins are not accepted by many governments because they can't track the transactions and can't put taxes on to it so many businesses are not taking it as a payment method. Currently, bitcoins are used mostly in online gambling and for some limited online activities.
Price volatility is the main reason why there are additional person uses bitcoin. Because of the price volatility in bitcoin, we have the opportunity to earn big.