bitcoin becomes very expensive one of them is due to the limited amount of currency, in addition to his many ads in various social media that tells that bitcoin will be a global currency is a factor that makes bitcoin very expensive
Basically, its prices are going up due to high demand and less supply. More and more businesses start accepting bitcoins for regular usage then its demand will go up but supply may not increase so fast so its prices will shot higher. The current prices may be looks expensive for now but after two or three years these prices may look very cheap so start investing in it instead of worrying about whether it is expensive or not.
Bitcoin is so expensive because of its nature. Decentralization makes it so popular. The government can't impose taxes in bitcoin. Bitcoin is a viable and tradable assets. It is very easy to trade and invest with a very low transaction fee.
The accessibility and popularity of bitcoin comes with the increase of its demand.