Bitcoin price fluctuates so much because it is still in development phase and nascent stage. There are many news and rumours around the legality of bitcoins. Common man is getting to know about bitcoin and thinking about investing in it.
There are lot of things happening in the bitcoin and crytpocurrency space. It is still like the little kid going up and down just for the fun of it.
Having said that I will list down some points that are effecting/effected the Bitcoin price:
Hacking of MtGox dropped the price of Bitcoin from $1200 to $400. Even now with DDOS attacks on Exchanges, bitcoin price gets effected by 6–10%
Japan and Australia declaring it a mode of payment. This shows countries are willing to trust Bitcoin as mode of payment
Internal war with Scaling issue going on. There are two groups in Bitcoin development who are divided on the course Bitcoin should take for the future. This is effecting the Bitcoins scalability and price heavily.
It is getting used in Illegal activities, Ponzis/MLM schemes. Every such incident negatively affects the price of the Bitcoin.
Common Man getting to know about Bitcoin and thinking to invest in it. My landord, a 50+ guy asked me about investing in Bitcoin. If such people started investing in Bitcoin all over the world, the price of bitcoin is sure to rise.
Similarly with every new Bitcoin development or negative news, the Bitcoin’s price gets effected. I have seen it drop down by 30% in a week and vice versa, majorly due to news and rumours.