The simple reason is to hope for a profit in the future, many people speculate about the future of bitcoin and many are optimistic bitcoin will replace real money such as dollar, euro, yen and many more.
I will agree and disagree at the same time. I agree with your first statement, recent studies shows immense ups in the rate of bit coin. Well I dont think bitcoin is any threat to other currencies. Its not gonna replace them. Bit coin is an opportunity why we treat it as a threat.
the opportunities that bitcoin have compel use to choose bitcoin. i do not think that there is any other investment from where one ca get such a good profit.