The answer to your question is simple, and it happens to be the fact that the bitcoin and other cryptocurrencies are decentralized,now what does that mean?, it simply means there is no body,rules,organization,government,insurance company nor Central Bank that acts as an overseer over this network/currency

This network/system/currency Is controlled only by the Individuals,users,enthusiast,investors etc in the system,only them can affect and influence the price/value in many ways, all depends on the demand/supply of the particular cryptocurrency coin
The blockchain technology happens to be the only institution/tecnology that has played this role somewhat as it is the technology on which this system is built,making use of cryptography and confirms/stores all transactions that take place on this network...The blockchain technology is the only indispensable institution of the BITCOIN