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.
The bitcoin cannot replace the fiat because that is the medium of the currency in the real world but I think by the end of the 21st century that is possible however, they should choose bitcoin because the bitcoin now is popular and have the high price and as time pass by the bitcoin price is increasing.