Honestly Bitcoin's market capitalization is very small (at about US $14 Billion) when compared to the large amount of fiat currency notes in circulation. This often leads to higher volatility cause bigger whales can infuse and dump a lot of cash causing the price fluctuations. There was this large infographic somewhere online that showed how small Bitcoin's market cap was compared to other currencies that show stable values when compared to Bitcoin's price. Also there's mostly no regulating authority to regulate it's price, but honestly we will never need one and over time naturally when there's more Bitcoins in circulation the market will become more stable. Infact the price of Bitcoin is more stable these days than it used to be.