There several factors that affects Bitcoin both positively and negatively such as government policy as rightly mentioned above, the forces of demand and supply of Bitcoin and other altcoins is another major factors that affects Bitcoin.
Market factors of all the cryptocurrencies are responsible for the increase or decrease in the price. We know that Altcoin price fluctuates with rise or fall in demand rate and same as Ethereum also follows this way, similarly the Bitcoin is also following this which is the common market controlling factor. The current market is suffering from low demand rate but do not panic and be optimistic about your upcoming huge profits.
Most of the reason why price fluctuates at worst situations, other altcoins specially from bounty campaign tokens dumped by hunters. It created more chaos on price as they sell both alts and bitcoin, that's why it really affects the bitcoin price as well due to more traders dumped at earlier time. Bitcoin price gone more volatile, when this situation happens and panic from investors might create diversions which mainly affects their decisions.