Speculation to answer your simple question. People is speculating that Bitcoin price will be pump due to its technology. This speculation gives value to the Bitcoin, the higher the expectations equals to the valuation of Bitcoin. This is same with other assets like gold, silver and real estates. People is the one defining the value lf the things based on its usability, availability and cost to generate or mine it.

But If you are asking the specific people who’s buying then you are asking an impossible things to be answered here.