I think the main reason why bitcoin value grows this fast is because popularity and acceptance of people to crypto currency is now getting wider also the trust over digital currency has been established that's why many investors are now looking towards into bitcoin. For almost a decade now bitcoin helps many people and some become successful and able to build their dreams into reality
It is definitely because of the massive and continuous flow of bitcoin investors. Many businesses accept bitcoin especially in e-commerce because they know that it is "worth accepting". The value will increase further in our digital age because as the internet and e-commerce continues to successfully revolutionize the market together with bitcoin, the demand with the cryptocurrency will definitely increase as well as its popularity. Even the 'ads' informing everyone about different cryptocurrencies invaded facebook (though we can never tell if it is legit), especially encouraging people to invest or mine bitcoin. That's the reason why it fluctuated this high in 2017, what more can we expect in the future years.