Bitcoin has value because bitcoin can also do what money can do. It can use as a form of payment where people find it useful in terms of buying or selling. Its value can be determined depends on how many people are willing to accept it as payment, the more people adopt it, the more its value will increase.
Not only that, but bitcoin can also solve fiat shortages related to the limited number of transactions and its ease without limitation of area and time. The decentralized system also attracted the interest of most people who wanted "freedom" and "transparency". The existence of market interest determines value. The rest, many people are still doubtful because it is full of pros and cons, trust-less. On the other hand, the offerings of technological advances are very promising, so this is a good niche to explore.