People buy cryptocurrency because they expect the price of cryptocurrency to rise in the next few years.
That's a mean reason why they still buying bitcoin because they expext what will happen in the future if they didn't follow what successful do, so they buy also ( including me ) 'cause when the price got increase they gain a profit from it. Moreover, bitcoin is a promising Coin that i've known, so no doubt i gain from it, not now but i think sooner or later.