Imagine you are living in the past, when gold had only industrial, probably jewelry use, and you invent the concept of money. Would you buy the gold then? Hint: industrial use accounts for maybe 1% of the price of gold.

That is what is happening with bitcoin, people realize it can have monetary use and buy it to capture the difference between intrinsic value (zero) and future monetary value. Of course, this can fail badly if bitcoin won't be used as money.

Additionally, there is a positive feedback mechanism that can be deadly for fractional reserve fiat currencies. People get credit, buy bitcoin, this inflates the fiat supply and drives bitcoin price higher, alluring more people to repeat the process. This process is called hyperbitcoinization.